Mechanisms of Prion Protein Aggregation - IngentaConnect

14

Protein & Peptide Letters, 2009, 16, 14-26

Mechanisms of Prion Protein Aggregation Sarah N. Fontaine and David R. Brown* Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath, BA2 7AY, UK Abstract: The prion protein is a cell surface glycoprotein that is converted to a protease resistant abnormal isoform during the course of prion disease. The normal isoform of this protein has been shown to be an antioxidant that aids the survival of neurones. The abnormal isoform is associated with both the transmissible agent of prion diseases and is also toxic. Recent studies have shown that there are multiple end states in terms of aggregation of the protein. Both soluble oligomers and insoluble fibrils can form from the abnormal isoform. Although fibrils are characteristic of the disease, the most infectious prions are associated with oligomers. Neurotoxicity can be associated with fibrils but mostly appears to be due to small aggregates. For many years fibrils were believed to be central to the disease process but currently evidence supports the notion that fibrils represent a "bulk" form of abnormal protein, which is largely inert, but carried along a small active component. This review will examine what is known about the mechanisms behind prion protein aggregation, and the relevance of each form for the disease.

Keywords: Prion, aggregation, fibril, oligomer, structure, neurotoxicity. INTRODUCTION Prion diseases, or transmissible spongiform encephalopathies (TSE), are a group of neurodegenerative diseases. These invariably fatal diseases include Cruetzfeldt-Jakob Disease, Gerstmann-Sträussler-Scheinker disease, fatal familial insomnia, kuru in humans, scrapie in small ruminants [1], bovine spongiform encephalopathy in cattle [2], chronic wasting disease in deer and elk [3], mink spongiform encephalopathy affecting mink [4], and feline spongiform encephalopathy in both wild and domestic cats [5, 6]. Additional TSE’s have been described in other animals including wild Bovidae species [7, 8] and non-human primates [9]. The causative agent of TSE’s is widely believed to involve a misfolded isoform of the cellular prion protein called a proteinaceous infectious particle or prion [10]. The cellular prion protein (PrPC) is an Asn-linked glycoslyated protein with two glycosylation sites as illustrated in Fig. (1). Studies show a homology in mammalian PrP structure: an unstructured N terminus consisting of residues 23-124, three -helices encompassing residues 144-154, 173194 and 200-227, and two short anti-parallel -strands containing residues 128-131 and 161-164 [11-17]. PrPC is attached to the outer cell membrane surface via a glycosylphosphatidylinisotol anchor [18, 19]. PrPSc, the disease associated isoform of PrPC, is structurally distinguishable from PrPC due to a higher content of -sheet structure [20-22]. In contrast to PrPC, PrPSc is not associated with the cell membrane, partially protease resistant, and digestion with proteinase K results in a protease resistant core termed PrP27-30 which corresponds to amino acids 90-231 [23-25]. PrPC is expressed ubiquitously with high expression levels in brain and lymphatic tissue. There is no consensus re *Address correspondence to this author at the Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath, BA2 7AY, UK; Tel:+44-1225383133; Fax:+44-1225386779; E-mail: [email protected] 0929-8665/09 $55.00+.00

garding function of PrPC, although evidence suggests it can act as an antioxidant, play a role in signal transduction, metal homeostasis, as well as a protective role against apoptosis (reviews: [26-28]). Despite controversy over its biological function, PrPC expression is required for disease pathogenesis. Transgenic PrP-/- mice and cattle do not develop prion disease when challenged with infectious scrapie, BSE, or TME [29-34]. PrP-/- animals have altered synaptic function [35], circadian rhythms [36], motor function [37, 38], copper metabolism [39] and impaired response to oxidative stress [40-42]. Evidence suggests that an aggregated form of PrPSc is in fact the key component in the disease [21, 43] but the precise character of the infectious aggregates is unclear. In vivo, PrPSc exists in aggregate depositions [44]. In humans, a proportion of these depositions are amyloid-like plaques, and these plaques differ in morphology depending on disease (reviewed in [45]). The presence of plaques or even PrPSc does not correlate to infectivity [46-50], however, it has been demonstrated that in vitro conversion ability does relate to infectivity [51]. Therefore, the study of in vitro aggregation of recombinant PrP is instrumental in providing insight into the mechanisms behind conversion from PrPC to PrPSc and aggregate accumulation, as well as to determine the conformation and species that is actually responsible for prion pathogenesis. This review focuses on the mechanism behind aggregation and examines the recent theories behind the toxicity of prion protein aggregates. FORMATION OF PrP AGGREGATES The first method used to study the conversion of PrPC to PrPSc was infection of cells in culture using infected brain homogenate. In these early experiments, successful infection of cells was then determined by subsequent inoculation of cell cultures into experimental animals [52-54]. The development of a cell free conversion assay utilising brain-derived PrPSc to convert PrPC purified from uninfected cell cultures © 2009 Bentham Science Publishers Ltd.

Mechanisms of Prion Protein Aggregation

Protein & Peptide Letters, 2009, Vol. 16, No. 1

15

Figure 1. Linear structure of unprocessed mouse PrP. Linear representation of the structure of mouse PrP. During processing in the ER, amino acids 1-23 are cleaved and oligosaccharides and a GPI anchor are added to the molecule.

to protease resistant PrP allowed for study of the factors which influences prion infection [55-57]. Using this method, Caughey et al. discovered that it was in fact aggregated PrPSc rather than the solubilised fractions which was able to convert PrPC to a protease resistant form [58]. This method, however, required large amounts of PrPSc and made it difficult to detect de novo conversion to PrP-resistant protein. Conversion of purified PrPC has also been demonstrated using infected brain slices [59], and cell extracts [60]. The development of the protein misfolding cyclic amplification method, PMCA, overcame the problem of using excess PrPSc. This method involves diluting a small amount of infectious brain homogenate into non-infected brain homogenate, resulting in a readily detectable level of PK resistant material that exceeds the amount initially added to the reaction, thus providing an easy method with which to monitor de novo PK resistant PrP formation [61]. More recently, a modified PMCA method has been described using recombinant PrP as the amplification substrate [62, 63]. As both versions of PMCA use brain derived PrPSc, it is impossible to eliminate whether any compounds co-purifying with the PrPSc are in fact necessary for the conversion reaction. Furthermore, it is impossible to determine what conformation of PrPSc causes the conversion. Recombinant PrP aggregates in vitro have been formed using various methods. Aggregation of the bacterially expressed, recombinant prion protein from a mostly -helical monomer can be induced by the addition of detergents [64], high pressure (reviewed in [65]), temperature (reviewed in [66]), low pH [67-69], by metal-induced conformation changes [70-72] and oxidation [73-75]. Additionally, partial denaturation of the protein can also lead to the accumulation of a -rich aggregated form of PrP [76]. It is interesting to note that PrP converts to a -rich form readily under conditions of acidic pH, much like those found in the endocytic pathway, a proposed site for PrPC - PrPSc conversion [20, 77, 78]. Therefore recombinant PrP is a useful tool in studying the conversion of PrPC to PrPSc and furthermore it is likely

the biophysical properties of recombinant PrP conversion may provide insight as to the pathology of the disease. Analysis of aggregated PrP is carried out using a variety of techniques including turbidometry, Fourier transform infrared spectroscopy (FTIR), circular dichroism spectroscopy (CD), electron microscopy, atomic force microscopy, and by the use of amyloid-binding dyes such as Thioflavin T (ThT), 8-Anilino-1-naphthalenesulfonic acid (ANS), Congo red, and Thioflavin S [79, 80]. These dyes bind exclusively to the common -sheet structures found in amyloid structures, and provide a useful tool for monitoring the formation of amyloid structures. ThT in particular binds exclusively to -rich 8-9A diameter cavities which run along the length of the fibril axis [81, 82]. ThT, commonly used as the emission wavelength upon binding to fibril-like structures (excitation 440 nm, emission 482 nm), is markedly different from that of the dye itself (excitation 350 nm, emission 438 nm) and also to the fluorescence pattern in water (excitation 440 nm, emission 493 nm) [80, 83]. ANS also has differential fluorescent patterns upon binding to different protein conformations [84, 85]. These dyes allow for sensitive measurement of the formation of fibrils. Aggregation of PrP has been modelled using three kinetic theories, illustrated in Fig. (2): template assisted-aggregation [86], nucleation-elongation polymerisation [87], and branched-chain polymerisation [88]. Each of these theories has been reviewed elsewhere, but in brief summary all employ the idea that a smaller unit of PrP (i.e., a nucleus, template or active centre) is responsible for further catalysing protein aggregation. In nucleation-dependant polymerisation, monomeric protein is the predominant species until a critical concentration is achieved and polymerisation to fibril precursors (nuclei) occurs. The length of time required for the fibril precursor nuclei to form is referred to as lag time [87]. Template assisted kinetics differs in that PrPSc acts as a template and upon binding to PrPC, recruits the normally folded molecule to refold into a PrPSc conformation [86, 89]. Finally, in

16 Protein & Peptide Letters, 2009, Vol. 16, No. 1

Fontaine and Brown

Figure 2. Prion protein aggregation kinetic models. Schematic illustrating the differences between the kinetic theories of PrP aggregation.

the theory of branched-chain polymerisation, the rate of the formation of end products is dependent on the number and polymerisation of active centres, as well as the volume of the reaction. Therefore, once the end product is formed, the “lag time” of the multiplication of active centres is reduced and the reaction proceeds until a plateau is reached [88]. As yet there is no conclusive evidence that any of these kinetic theories is the correct model. Both branched-chain and nucleation-elongation dependent polymerisation exhibit sigmoidal kinetic curves, as seen experimentally, and both account for the unknown nature of the structure of the seed or active centre which initiates the aggregation of the protein and correlates to the infectious prion. It has been suggested that the formation of smaller oligomeric structures in misfolding pathways are the key components to prion diseases [76, 90-93] and that these intermediates are in fact the molecule responsible for infection [94]. Initially it was supposed PrP formed distinct, -rich oligomers prior to amyloid formation [76] but data now seems to support the idea that -oligomers are not on the pathway to amyloid fibrils, but rather exist in a dynamic state with helical monomers [92, 95-99]. -structures formed under acidic conditions have different properties than those formed under neutral conditions—that is, -oligomers formed at acid pH do not have amyloidal characteristics [97, 100]. Additionally it has been shown that the ability to fold into a rich structure is not exclusive to neurodegenerativeassociated proteins, but rather a property of proteins in general [101].

Therefore, it is clear the pathway of prion protein aggregation is complex and occurs potentially through several intermediate steps. Several models of the prion protein aggregation pathway have been proposed. Fig. (3) highlights the amalgamation of the most likely of pathways. -oligomer structure arises from a non-amyloid pathway, wherein the protein forms amorphous, –structure rich aggregates which then order into spherical -oligomers. On the pathway to amyloid fibril formation, a proposed pre-amyloid intermediary is a reversible, mainly -helical structure which may be in equilibrium with the native monomer [95]. This intermediate state then proceeds to a dimer stage, where the formation of intermolecular bonds results from domain swapping of helix 3 [102] or alternatively through the formation of an ordered -helical state with intramolecular bonds between residues 90-152, 90-196, 90-202 [103]. Dimerisation has been shown to be a crucial if not initiatory step in fibrillization [104-107]. From the dimer formation, acquisition of sheet content leads to growth of protofilaments to protofibrils, and finally to mature fibrils. The common structure of amyloid fibrils consists of a cross spine containing a double sheet of stacked, parallel -rich segments. These segments stack in a head to tail structure, and are bound to their neighbour via side chains which act like a zipper, using hydrogen binding and interactions between the backbones to form the structure [108-113]. In mammalian prions, the cross -core correlates to amino acids 127-230 [114-116] and the N-terminal tail, including the hydrophobic region of PrP, has been shown to be at the surface of fibrils as determined by antibody mapping [117].



17

Figure 3. Schematic representation of prion aggregation pathways. The exact toxic conformer of PrP is unknown but possibilities are illustrated above. In the amyloid pathway, monomeric -helical PrP exists in a dynamic state with a mostly -helical intermediate. This intermediate upon dimerization gains B-sheet structure and proceeds to form mature amyloid fibrils. These fibrils may be subjected to fragmentation, wherein they either act as a toxic molecule or feed back into the amyloid formation pathway. Alternatively, gain of -sheet structure of PrP monomers leads to the formation of amorphous -sheet rich aggregates which then order into globular oligomers.

Many suggestions have been proposed concerning the extent of structural rearrangement that occurs during prion conversion, although at present data is conflicting. It has been proposed that the C-terminal domain of PrP undergoes major rearrangement during conversion to an amyloid form [116]. Alternatively, the C-terminal region retains -helical conformation, while either four regions spanning 116-119, 119-132, 135-140, and 160-164 assemble into a -sheet [118] or residues 89-175 assemble into 3 left handed helices [90]. Helix 1 of PrP may be important for aggregation [119-121], although its role is unclear as it may not convert to a -sheet form [120] and it is stable over a range of pH values and solvent conditions [122-124]. There is the potential that the formation of asparagine-arginine salt bridges in helix 1 stabilise PrP and form intermolecular bonds with other PrP molecules [125] which could lead to aggregation, in contrast however the bridges appear to stabilise PrPC in vitro [123]. It has therefore been suggested that the specific orientation of charged residues within helix 1, particularly the C-terminal end of helix1, is essential for conversion. This data corroborates with the recent observation that interactions between the glutamic acid at 196, aspartic acid at 202 and glycine residue at 90 may be important for dimer formation [103]. However, molecular dynamics and experimental evidence suggest helix 2 and 3 are mainly responsible for the conformational change to pre-PrPSc intermediates. The later half of helix 2 (residues 184-194) and parts of helix 3 spanning residues 200-204 and 215-223 are inherently less stable and more prone to change conformation[126]. Recently Fitzmaurice and colleagues have shown the domain corresponding to 119-130 of classical sheep scrapie PrP must interact with the helix2-3 turn in order for

extended -sheet formation to occur [127] leading to the suggestion that the ease of unwinding helix 2 could modulate the folding intermediates. The importance of the turn between helix 2 and 3 is further consolidated by investigation into the cross -core of PrP fibrils, which has been shown to encompass amino acid residues 127-230 [114-116]. The data seems to support the likelihood that the C-terminus of PrP does indeed undergo a conformational change and potentially contains a modulatory feature which directs the degree of -folding during aggregation. Additionally, the Nterminal region modifies PrP aggregation [128], but is not necessary for aggregation to occur as numerous studies use an N-terminally truncated PrP. Therefore, as the definite structure of PrPSc is still unknown, it is impossible to rule out the relevance of observations published by other studies in terms of conformational rearrangements of the flexible Nterminal region during aggregation. INFLUENCE OF DISEASE–ASSOCIATED MUTATIONS/POLYMORPHISMS ON AGGREGATION There are more than 20 mutations related to human prion diseases (reviewed in [129]), the most common mutations world wide are E200K, D178N, P102L and octapeptide repeat insertions. Human PrP exists in two allelic forms with a polymorphism at amino acid position 129. This polymorphism has been linked to disease susceptibility in acquired prion diseases such as kuru, variant CJD and iatrogenic CJD [28, 130-135]. Therefore, investigation of the different alleles on both the structure of PrPC and on aggregation has been studied. Analyses indicate that the polymorphism of human PrPC has no effect on the globular structure or stabil-


ity [136]. The codon 129 polymorphism also has no effect on the ability of the protein to be convert into a -sheet rich PrP or bind copper [137, 138]. However, it has been shown that the initial folding state of the protein defines the kinetics of the conversion reaction [139-142]. While there are no differences between the allelic forms in conversion of monomeric human PrP to amyloid under non denaturing conditions, [136, 141, 143], under denaturing conditions there are differences. PrP with a methionine at 129 has a more exposed helix 1 and is more prone to form -rich oligomers and to aggregate [140, 144]. Aggregation of PrP with a valine at 129 gains -sheet structure more rapidly than methionine 129 (a lag time of 12 h compared with 24 h), and has a shorter lag time although the rates of amyloid growth does not differ between the two [142]. The more rapid acquisition of sheet structure by the valine allelic form is supported by molecular dynamic modelling studies [145]. In contrast, Weber et al. found that while in denaturing conditions, M129 was readily able to form amyloid fibrils, V129 form was unable to do so, even after an extended period[138]. This discrepancy indicates the differences in solvent and denaturing conditions can affect the aggregation of the protein, which in turn suggests the importance of the surrounding environment in prion aggregation. In addition, there are many other pathogenicallyassociated mutations whose effects aggregation and amyloid formation have been described. The commonly found mutation D178N has been shown to be modulated by allelic form of PrP at codon 129, and in comparison to wild type protein, the mutation containing polymorphic alleles of recombinant PrP90-231 have a greater tendency to form amyloid fibrils at neutral pH and -oligomers at acidic pH [146]. Recombinant protein with another disease-associated mutation, F198S, also has a higher propensity for aggregation than wild type protein [147]. Furthermore, these pathological mutations appear to increase the propensity of monomeric folding intermediates and these folding intermediates again may be important in the pathway to amyloid formation [148, 149]. The polymorphism at 129 was also shown to affect the structure but not the aggregation of a C-terminally truncated PrP containing N-terminal pathological mutations [150]. The lack of effect on aggregation could be due to the absence of the C-terminal region which has been shown to undergo the most rearrangement during conversion and therefore a peptide lacking this region would not be a true representative of the effect of the polymorphism on the full length protein. Another common pathological mutation associated with prion disease is the insertion of extra octapeptide repeats within the N-terminal region. PrP with these insertion mutations has an increased propensity to aggregate which is proportional to the number of insertions [121, 151-153], although a yeast model comparing similar insertions found the resulting fibrils are less stable [154]. In cell culture, extra octapeptide repeats leads to increased aggregation and increased protease resistance[155]. It is therefore clear the Nterminal region plays a role in mediating aggregation, even though it is not specifically required for aggregation. In addition, this region has been shown to modulate binding of ligands in the C-terminal region [156] and aggregation in pH dependent manner [128, 157].

Fontaine and Brown

In addition to variations in human PrP aggregation, variations in aggregation of different sheep alleles of PrP have been shown. Cell-free conversion of different allelic forms of ovine PrP mimicked scrapie susceptibility in vivo. The most susceptible allelic form, VRQ, had the highest rate of conversion to a protease resistant form of PrP, where the allelic form associated with scrapie resistance had a limited ability to form protease resistant PrP in the study [158, 159]. Scrapie-resistant ovine PrP alleles have decreased -sheet content in aggregation intermediates when compared to scrapiesusceptible allele [70], and copper-induced structural changes appear to be modulated by the ovine polymorphism M112T, where M112 (ARQ) ovine PrP appears to be more thermostable but has a higher -sheet content [160]. Thus, study of the structural characteristics induced by polymorphisms and pathological mutations provide insight not only into the mechanism of prion aggregation, but potentially explain the differences in pathogenicity seen between various diseases [161] as well as the susceptibility of specific polymorphisms to these diseases. FACTORS AFFECTING PRION PROTEIN AGGREGATION Metals, polyanionic compounds, gycosaminoglycans, and dendrimers have all been shown to influence the aggregation of PrP peptides and full length protein. Metals PrPC has been shown to bind copper as well as other metals such as manganese, nickel, and zinc, both within the Nterminal octapeptide repeat region and within the hydrophobic region [39, 162-165]. In addition, these metals are able to impart structural changes to PrP. There is a wealth of evidence indicating that the addition of copper to recombinant PrP induces a conformational change which leads to the adoption of PrPSc–like properties, including increased sheet content, decreased -helical content, and PK resistance. [71, 163, 166-173]. Polymorphisms can influence the degree to which copper can induce -sheet structure, for instance, the scrapie-susceptible ovine allele VRQ has a greater increase in -sheet structure in aggregate intermediates when compared to the scrapie-resistant ARR allele [70]. This copper-induced conformational change is mediated by the presence of the N-terminal region of PrP [174] and is thought to be due to the differences in helix 1 and residue 171 [175]. The actual effect of copper on aggregation is contradictory, as the addition of Cu2+ has been shown to inhibit aggregation [176-179] and cell-free conversion [180] but can also initiate aggregation of recombinant protein [70, 72-74, 127, 181, 182]. Copper, however is not the only metal which causes such contrasting effects on PrP. In contrast, Zn2+ inhibited aggregation of PrP under denaturing conditions [177] and cell-free conversion using purified PrPC [180], although it promoted aggregation of a shorter peptide PrP82-146 [178] and though it did not cause an increase in -sheet structure, it increased the PK resistance of the protein [183]. Copper and zinc have been shown to modulate the aggregation and toxicity of the PrP106-126 fragment [184]. It is interesting to note that the cations which have an inhibitory effect on PrP aggregation are also those which can induce internalisation of PrPC [185-188].


Manganese has been shown to bind to PrP, even when copper is bound [189] and this manganese-bound PrP is protease resistant [163, 190]. Manganese-loaded PrP has been shown to initiate aggregation of PrP [163, 176, 191, 192]. The initiation of aggregation is due to the structural change manganese confers on PrP once bound [163], similar to the manner that copper causes a conformational change. Therefore the only effect manganese can produce on aggregation is as a seed or initiator of aggregation and does not influence aggregation beyond the initial stages. This is corroborated with the findings that manganese delayed the aggregation of PrP82-146 [178] and does not affect cell-free conversion [180] wherein purified PrP27-30 derived from infected brain homogenate is used to convert purified PrPC. This lack of effect by manganese would be due to the inability of manganese to bind to and confer a conformational change to PrP2730 as it exists as aggregates. Manganese also does not affect aggregation of partially denatured PrP [177] which may be attributed to manganese being unable to bind to the denatured protein properly. Manganese is not the only metal which can promote aggregation, as cobalt has been shown to have this affect also [176]. The inhibitory effect of copper on PrP aggregation could result from a number of reasons, such as the pH of the reaction, as it has been well documented that pH affects copper binding [193]. Additionally the method of PrP purification and the buffers used have been shown to affect the aggregation of PrP, and most likely the manner in which PrP binds and interacts with metals. Perhaps most importantly, the starting conformation of the protein may be essential in delineating the differences in the effects of metals on PrP. If the conformation is such that the metal cannot effectively bind to PrP, the resulting effects will be markedly different than those obtained from a conformation which is freely able to bind metals. Studies on metal induced fibrillization of A, for example, indicate that access to different degrees of metal ion coordination may regulate the effect of metals on fibril assembly [194]. Therefore the most likely explanation for the conflicting effects of metals on prion protein aggregation lies within the protein-metal interactions. The involvement of metals with PrP is important as it has been suggested that metals, in particular copper, play a role in the normal function of the prion protein [193]. Therefore the interaction with metals in the aggregation process could be instrumental in understanding the disease pathogenesis. Glycosaminoglycans, Polyanions, and Other Compounds More recent research has indicated that RNA, polyanions and glycosoaminoglycans (GAGs) stimulate cell-free conversion of synthetic peptides, recombinant and brain-derived PrP into a protease resistant form of PrP [195-199]. These results are in contrast to the aggregation data of Perez et al. [200] who found GAGs inhibited fibrilization of the peptide PrP106-126. However, the evidence nearly entirely supports the idea GAGs do increase the aggregation of PrP. This may be particularly relevant to disease pathogenesis, as it has been shown that GAGs can bind recombinant PrP [201, 202], and they are essential for prion replication [203, 204]. The stimulating effect GAGs have on aggregation also agrees with data on other neurodegenerative diseases. The aggregation of synucleins of Parkinson’s disease and A of Alz-


19

heimer’s disease has also been shown to be stimulated by the addition of heparin and other GAGs [205-207]. The polyanion Congo red (CR) has been shown to inhibit conversion of PrP in vitro at high molecular ratios [208-210] and at low molecular rations promote aggregation [211]. This effect could be explained by the fact CR does not act upon pre-existing PrPres molecules [212], further supported by the evidence that CR delays the onset of prion disease in vivo [213-215] . CR has been shown to inhibit aggregation by promotion of a more denatured state [216]. Interestingly, in vitro, CR derivatives have been shown to clear PrPSc aggregates by preventing the inhibitory activity of PrPSc on the ubiquitin proteasome system (UPS) [217], which implies that the mechanism by which CR extends the incubation period of the disease could be attributed to promotion of UPS activity to a certain extent by denaturing protein aggregates. CR inhibition is not prion-specific as it has been demonstrated that CR inhibits aggregation of A peptides [218, 219]. Additionally, branched polymers called dendrimers have been shown to modulate aggregation of PrP peptides by inhibiting or slowing aggregation, modulating the amount of fibrils produced and rendering the resulting aggregations more protease-sensitive [220-222]. A phenolic compound called curcumin has been shown to inhibit PrP conversion in vitro and in cell culture [223], as well as inhibiting aggregation of -synuclein [224] and A [225], and has recently been shown to bind only to amyloid forms of PrP [226]. In addition, numerous other polyphenols [227] and antibodies [228] have been postulated to prevent accumulation of aggregates in neurodegenerative disease. The effects of compounds that may prevent or intervene in protein aggregation deserve further investigation. An intervention strategy utilizing these types of compounds could hopefully yield effective therapies for treatment of prion and other protein aggregation diseases. TOXIC PRION FIBRILS

PROTEIN

OLIGOMERS

AND

The idea that small oligomers are in fact the culprit in prion disease initially arose from the suggestion that the infectious form of PrP was around 50-150 kDa in size [229232] and later suggestions that a minimal infectious unit corresponded to 600 kDa [233]. It was then discovered by dissociation of PrPSc aggregates that the most infectious PrP aggregates were round spherical oligomers, 17-27 nm in length and 300-600 kDa in size, corresponding to 14-28 PrP molecule units [234]. Study of a pathway producing wellordered -oligomers of PrP has shown they consist of the equivalent of 25 monomers of PrP, supporting the idea of the oligomer as the minimal infectious unit [73]. Although the size of oligomers can vary depending on the experimental conditions under which they were produced, a similarity in the roughly spherical, globular shape of oligomers is seen in prion misfolding pathways [73, 100, 181, 235]. There is an intriguing idea that fibril fragmentation may contribute to PrP toxicity in vivo. While evidence does not correlate infectivity with plaque formation[46], it has been proposed that fibrils may act as reservoirs of infectious units [99, 232, 236]. Studies using small peptides of PrP, aggregated in -sheet structures (see Fig. (4)), have been shown to


Fontaine and Brown

Figure 4. Electron micrographs of PrP peptide fibrils. Negative staining shows fibrils formed from peptides A) PrP106-126 and B) PrP127147.

cause neurotoxicity [237-239]. If stability of fibrils is a protective mechanism [240], it is logical that sequestration of aggregated proteins into a lower energy, highly ordered state such as a fibril would “trap” any infectious particles. However, the intrinsic fragility of fibrils due to the conformation of the C-terminus gives rise to the possibility that once fibrils and plaques are formed, there is a danger of fragmentation over time thus giving rise to more infectious units capable of propagating the disease, which has been shown previously to occur with yeast prions [241]. Fragmentation of mammalian prions could potentially be due to small heat shock proteins, lipid interactions, or surface adhesion-induced mechanical stress [114, 242, 243]. It has been established that PrPSc is toxic to cells and that synthetic and recombinant prion protein peptides exhibit neurotoxcity [237-239]. However, it has previously been difficult to ascertain whether the cause of toxicity was due to the structure of the peptide, as the most commonly used peptide PrP106-126 is toxic itself without aggregation. Recent evidence indicates that both prion oligomers and fibrils, both rich in -sheet content, have been shown to be toxic in vivo and in vitro. Soluble N-terminally truncated PrP (90-231) rich in -turns was first shown to cause increased toxicity to culture neuroblastoma cells when compared to treatment with high molecular weight aggregates or -helical PrP [244]. Both -oligomers and fibrils created from full-length recombinant were toxic in vitro to both neuroblastoma cells and primary neurons [245]. Fibrils were more toxic than the -oligomers in cultured cells, although in primary hippocampal and cerebellar neurons -oligomers were slightly more toxic. Both conformations caused high (80-90%) levels of cell death by apoptosis [245]. Aggregation of Nterminally truncated PrP90-231 to a -rich form caused apoptotic cell death when applied to human neuroblastoma cells in culture [246, 247]. This cell death was mediated by p38 and caspase 3 activation [246, 247]. Further study into

the toxic conformation of the N-terminally truncated PrP90231 indicated a -rich soluble monomer or small oligomer was more toxic to neuroblastoma cells than larger -rich aggregates and fibrils, and these smaller oligomers had a marked increase in cellular uptake into lysosomal compartments when compared to both -monomeric and large aggregates [248]. The toxic -oligomers had an increased exposure of the hydrophobic region, consistent with other published data indicating the hydrophobic region is more exposed in aggregates and may modulate the toxicity of the oligomers [249]. In further study, fibrils shown to be more toxic than -oligomers or monomeric, -helical PrP when exposed to glial- or neuronally-differentiated NT2 cells[250]. The differentiated cells treated with fibrils also showed more neuronal impairment including development of neuritic beads and changes to the distribution of the synapse specific protein synaptophysin [250]. These results are in accordance with previously published results showing loss of synaptic function in early prion disease [251]. The disagreement as to whether -oligomers are more toxic than amyloid fibrils may stem from the fact cells respond to diverse protein conformations in different ways. It was shown that -oligomers induced wide-spread apoptosis, whereas amyloid fibrils induced cell aggregation around the fibrils and then apoptosis [245]. Novitskaya et al. postulated that cells can recognise and respond to the differences between conformations, which would account for the differences in toxicity seen in these studies. Indeed, it has been suggested that differences in toxicity may be due to the different suprastructure of the PrP aggregates, in regards to the degree of which domains are buried or exposed on the surfaces of the these aggregates [249]. The differences could also be due to preparation of the oligomers, as they differed between the studies and therefore the end oligomeric products would not be identical. Additionally, the use of a recombinant protein, which lacks any post-translational modi-


fications, would not completely mimic the folding and misfolding situation in vivo, especially as molecular chaperones are generally involved in protein folding and trafficking. Thus, exposure of the protein to the processes related to purifying and appropriately refolding a recombinant protein may result in differences in regards to protein aggregate toxicity in vitro. It has been suggested that oligomer toxicity is not specific to PrPC expression. Simoneau et al. 2007 demonstrated application of PrP fibrils to primary murine cortical neurons resulted in no toxicity, whereas both ovine and murine PrP -oligomers were toxic and caused apoptosis-mediated death. Fibrils were toxic in vivo, but markedly less toxic than the -oligomers [249]. However, these PrP oligomers and fibrils were also toxic on PrP-/- cells and PrP-/- mice, so it is difficult to ascertain the biological action of the oligomers produced by this group. In contrast, the study by Novitskaya et al. 2006 found PrPC expression was required for the toxicity caused by PrP -oligomers and fibrils. The use of small interfering RNA to knock-down expression of PrP in cells subsequently reduced the toxicity of both fibrils and oligomers in those cells [245], in agreement with published knowledge that endogenous PrPC is necessary for the effect of PrPSc [252]. Whilst it has been shown PrPC expression was not required for toxicity of a cytosolic form of PrP which has been theorised to be the toxic form of PrP [253] it does beg the question whether toxicity regardless of PrPC expression is relevant to prion pathogenesis. There is potential the toxicity of the oligomers of the Simoneau et al. study is due to the presence of oligomers themselves and not to the effect on endogenous PrPC. It has been shown that oligomers from non-disease related protein can cause cell death [254] and even induce neurodegeneration [255], which indicates a common mechanism of toxicity with oligomeric proteins due to shared structural features. This hypothesis is supported by the invention of antibodies which detect solely oligomeric aggregates, and mediate toxicity of A oligomers as a therapeutic approach [256]. Along with the recent advent of fibril specific antibodies [257], these conformation dependent antibodies will allow for more detailed dissection of protein folding pathways and could be used to determine with more specificity the infectious form of PrP. Evidence that PrP toxicity is mediated by apoptosis is well documented. Cells that are persistently prion-infected undergo apoptosis [258] and additional evidence indicates PrP aggregates are indeed toxic as covalently cross-linked PrP triggers apoptosis [259]. While it is know that oligomers PrP induce apoptotic cell death, the mechanism by which this occurs is not yet fully understood. Work on A oligomers has suggested that oligomers may form pores in membranes [120] and the disruption of membranes may be the cause of oligomer toxicity [260]. An alternative mechanism is that the accumulation of oligomers and aggregates alters endoplasmic reticulum (ER) homeostasis and thus triggers apoptosis by the alteration of ER signalling pathways [261]. Oxidative stress caused by protein accumulation has been demonstrated previously [262, 263] and it well established that oxidative stress increases with ageing [264], which is when neurodegenerative diseases usually manifest.


21

Oxidative damage to RNA has been shown to occur at the very early stages of neurodegenerative disease [265] and this may occur as a result of oligomer toxicity. In addition, exposure of recombinant PrP to conditions mimicking those of oxidative stress resulted in an increase in -sheet structure, PK resistance, and the ability to act as a seed in aggregation reactions, suggesting oxidative damage could enhance the progression of prion disease [240] which would then contribute to activation of apoptosis signalling cascades. Another probable theory is that the intracellular accumulation of oligomers saturates the proteasome system and initiates apoptosis. It has been well documented that the function of the proteasome is impaired in the neurodegenerative disorders, during aging, and by the presence of aggregates [266268]. Furthermore the proteasome cannot effectively degrade large amounts of aggregated protein [269]. The UPS is involved in turnover of wild type PrP [270] , and it was initially proposed that altered PrPC trafficking due to toxicity impairs the function of the UPS, leading to accumulation of PrP aggregates and apoptosis[271]. The function of the UPS is impaired in prion-infected cells, resulting in the accumulation of cytosolic aggresomes containing PrPSc, ubiquitin, heat shock protein 70, proteasome subunits and vimentin [272]. These aggresomes appeared to be neurotoxic and activate caspase 3 and 8 dependent apoptosis [272], in agreement with previously reported activation of caspase 8 in response to aggregates of HD and AD [273, 274]. Perhaps the most compelling evidence for the impairment of the UPS as a mechanism by which oligomers toxicity acts, comes from the finding that PrP -oligomers, but not amyloid fibrils, inhibit the activity of the 26S proteasome [275]. This inhibition was specific only to -oligomers, as use of oligomer-directed antibodies resulted in an abrogation of the inhibition effect [275]. Inhibition of UPS activity in response to prion infection was demonstrated using a GFP-reporter system in transgenic mice, thereby demonstrating the impairment of the UPS during prion infection in vivo [275]. Interestingly, oxidative stress has been shown to cause damage to the 26S proteasome, making it less effective at degrading misfolded or damaged cytosolic protein (review in [264]). This suggests both oxidative damage and proteasome dysfunction resulting in apoptosis could be mechanisms of oligomer toxicity. Work on other neurodegenerative diseases has shown the importance of pre-fibrillar oligomers in disease pathology. Published work with AD has shown that small A oligomers interfere with synaptic function and cause reversible loss of cognitive function in mice [276, 277]. Additionally, specific A oligomers have been shown to cause early memory loss in Tg2576 mice [278], which is a transgenic mouse model of AD. A oligomers have also been shown to cause an increase in oxidative stress, as well as disrupting synaptic plasticity and calcium homeostasis (reviewed in [279]). GENERATION OF INFECTIOUS PRP IN VITRO There has been little success in generating de novo prion infectivity from recombinant prion protein, as only a single study has been published reporting this. Amyloid fibrils were formed from N-terminally truncated murine PrP89-231 and then inoculated into transgenic mice expressing sixteen times more PrP than wild type. Results indicated the fibrils had


quite low infectivity when inoculated into mice, with extended disease incubation periods ranging in length from 380 to 660 days. Subsequent transmission into either wild type mice or transgenic mice expressing eight times more PrP than wild type, shortened the incubation period considerably [280]. To date, however, these results have not been replicated. More success with producing infectious PrP in vitro has emerged from the use of PMCA to generate infectivity using brain homogenates as substrates. Inoculation of the PMCA-generated material into animal bioassays produced only low infectivity in vivo [281-284]. It has been postulated the reason for the low infectivity is due to the sonication process, which tends to break PrPSc into very small aggregates which can be cleared by the brain [284], but when this PMCA-derived material is applied to cultured cells, the ability to convert to PrPSc is enhanced, which then suggests that these small PrPSc aggregates are responsible for conversion activity [283]. Adsorption of these small aggregated particles to nitrocellulose has been shown to enhance the infectivity, potentially by excluding them from clearance from the brain [283, 284]. It is difficult to discern the exact influences of PrP alone when using brain homogenate, as many other components besides PrP are present and these factors may manipulate PrP conversion. To an extent this has been addressed by using purified brain-derived PrPC as a substrate in PMCA, as purified PrPC has been shown to form proteaseresistant material in vitro and has recently been shown to possess infectivity in a hamster model [285]. While PKresistant material produced by the PMCA has been shown to be infectious in vivo, the involvement of other compounds in the system in prion conversion has not been fully elucidated. CONCLUSION It is imperative that the conformation of the infectious prion molecule be determined in order to propose a definitive model of aggregation and for further research to provide a fuller understanding of protein-misfolding diseases. Development of technologies that will allow study of in vivo PrPSc aggregates will be essential for determining the conformation, and the identity of the toxicity-associated PrP structure. However, elucidation of the normal function of PrP is tantamount to understanding the nature that the role of disease associated mutations, lipids, metals, and polyanionic compounds have on the aggregation and formation of infectious PrP. This is essential to developing successful intervention strategies and therapies.

Fontaine and Brown

GSS

= Gerstmann-Sträussler-Scheinker disease

TME

= Transmissible Mink Encephalopathy

UPS

= Ubiquitin proteasome system

CR

= Congo red

AD

= Alzheimer’s Disease

HD

= Huntingtin’s Disease

PD

= Parkinson’s disease

GAG

= Glycosaminoglycan

ER

= Endoplasmic reticulum

PMCA = Protein misfolding cyclic amplification PrPres

REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18]

[19]

ACKNOWLEDGEMENTS The authors wish to thank Dr. J.A. Wright for critical reading of this manuscript. ABBREVIATIONS PrP

[20] [21] [22] [23]

= Prion protein = Cellular prion protein

[24]

PrPSc

= Scrapie prion protein PK proteinase K

[25]

ThT

= Thioflavin T

TSE

= Transmissible spongiform encephalopathies CJD Cruetzfeldt-Jakob Disease

PrP

C

= Protease resistant PrP

[26]

M’Faydean, J. (1918) J. Comp. Pathol. Ther., 31, 278. Wells, G.A., Scott, A.C., Johnson, C.T., Gunnung, R.F., Hancock, R.D., Jeffrey, M., Dawson, M. and Rodlers, R. (1987) Vet. Rec., 121, 419. Williams, E. S. and Young, S. (1980) J. Wildl. Dis., 16, 89. Marsh, R. F. and Hadlow, W. J. (1992) Rev. Sci. Tech., 11, 539. Wyatt, J. M., Pearson, G. R., Smerdon, T. N., Gruffydd-Jones, T. J., Wells, G. A. and Wilesmith, J. W. (1991) Vet. Rec., 129, 233. Willoughby, K., Kelly, D. F., Lyon, D. G. and Wells, G. A. (1992) Vet. Rec., 131, 431. Kirkwood, J. K., Wells, G. A., Wilesmith, J. W., Cunningham, A. A. and Jackson, S. I. (1990) Vet. Rec., 127, 418. Jeffrey, M. and Wells, G. A. (1988) Vet. Pathol., 25, 398. Sigurdson, C. J. and Miller, M. W. (2003) Br. Med. Bull., 66, 199. Prusiner, S. B. (1982) Science, 216, 136. Calzolai, L., Lysek, D. A., Guntert, P., von Schroetter, C., Riek, R., Zahn, R. and Wuthrich, K. (2000) Proc. Natl. Acad. Sci. USA, 97, 8340. Lopez Garcia, F., Zahn, R., Riek, R. and Wuthrich, K. (2000) Proc. Natl. Acad. Sci. USA, 97, 8334. Zahn, R., Liu, A., Luhrs, T., Riek, R., von Schroetter, C., Lopez Garcia, F., Billeter, M., Calzolai, L., Wider, G. and Wuthrich, K. (2000) Proc. Natl. Acad. Sci. USA, 97, 145. Riek, R., Hornemann, S., Wider, G., Billeter, M., Glockshuber, R. and Wuthrich, K. (1996) Nature, 382, 180. Riek, R., Hornemann, S., Wider, G., Glockshuber, R. and Wuthrich, K. (1997) FEBS Lett., 413, 282. Riek, R., Wider, G., Billeter, M., Hornemann, S., Glockshuber, R. and Wuthrich, K. (1998) Proc. Natl. Acad. Sci. USA, 95, 11667. Donne, D. G., Viles, J. H., Groth, D., Mehlhorn, I., James, T. L., Cohen, F. E., Prusiner, S. B., Wright, P. E. and Dyson, H. J. (1997) Proc. Natl. Acad. Sci. USA, 94, 13452. Lysek, D. A., Schorn, C., Nivon, L. G., Esteve-Moya, V., Christen, B., Calzolai, L., von Schroetter, C., Fiorito, F., Herrmann, T., Guntert, P. and Wuthrich, K. (2005) Proc. Natl. Acad. Sci. USA, 102, 640. Gossert, A. D., Bonjour, S., Lysek, D. A., Fiorito, F. and Wuthrich, K. (2005) Proc. Natl. Acad. Sci. USA, 102, 646. Caughey, B., Race, R. E., Ernst, D., Buchmeier, M. J. and Chesebro, B. (1989) J. Virol., 63, 175. Stahl, N., Borchelt, D. R., Hsiao, K. and Prusiner, S. B. (1987) Cell, 51, 229. Caughey, B. (1991) Curr. Top. Microbiol. Immunol., 172, 93. Pan, K. M., Baldwin, M., Nguyen, J., Gasset, M., Serban, A., Groth, D., Mehlhorn, I., Huang, Z., Fletterick, R. J. and Cohen, F. E. (1993) Proc. Natl. Acad. Sci. USA, 90, 10962. Safar, J., Roller, P. P., Gajdusek, D. C. and Gibbs, C. J., Jr. (1993) J. Biol. Chem., 268, 20276. Meyer, R. K., McKinley, M. P., Bowman, K. A., Braunfeld, M. B., Barry, R. A. and Prusiner, S. B. (1986) Proc. Natl. Acad. Sci. USA, 83, 2310. Oesch, B., Westaway, D., Walchli, M., McKinley, M. P., Kent, S. B., Aebersold, R., Barry, R. A., Tempst, P., Teplow, D. B., Hood, L. E., Prusiner, S. B. and Weissmann, C. (1985) Cell, 40, 735.

Mechanisms of Prion Protein Aggregation [27] [28] [29] [30] [31] [32] [33] [34] [35] [36]

[37] [38] [39] [40] [41]

[42] [43] [44] [45] [46] [47] [48]

[49] [50] [51] [52]

[53] [54] [55] [56] [57] [58]

McKinley, M. P., Meyer, R. K., Kenaga, L., Rahbar, F., Cotter, R., Serban, A. and Prusiner, S. B. (1991) J. Virol., 65, 1340. Hu, W., Rosenberg, R. N. and Stuve, O. (2007) Acta Neurol Scand, 116, 75. Brown, D. R. (2001) Brain Res. Bull., 55, 165. Collinge, J. (2001) Annu. Rev. Neurosci., 24, 519. Weissmann, C., Bueler, H., Fischer, M., Sailer, A., Aguzzi, A. and Aguet, M. (1994) Ann. N.Y. Acad. Sci., 724, 235. Weissmann, C., Bueler, H., Fischer, M., Sauer, A. and Aguet, M. (1994) Philos. Trans. R. Soc. Lond. B. Biol. Sci., 343, 431. Prusiner, S. B., Groth, D., Serban, A., Koehler, R., Foster, D., Torchia, M., Burton, D., Yang, S. L. and DeArmond, S. J. (1993) Proc. Natl. Acad. Sci. USA, 90, 10608. Bueler, H., Aguzzi, A., Sailer, A., Greiner, R. A., Autenried, P., Aguet, M. and Weissmann, C. (1993) Cell, 73, 1339. Sakaguchi, S., Katamine, S., Shigematsu, K., Nakatani, A., Moriuchi, R., Nishida, N., Kurokawa, K., Nakaoke, R., Sato, H. and Jishage, K. (1995) J. Virol., 69, 7586. Richt, J. A., Kasinathan, P., Hamir, A. N., Castilla, J., Sathiyaseelan, T., Vargas, F., Sathiyaseelan, J., Wu, H., Matsushita, H., Koster, J., Kato, S., Ishida, I., Soto, C., Robl, J. M. and Kuroiwa, Y. (2007) Nat. Biotechnol., 25, 132. Collinge, J., Whittington, M. A., Sidle, K. C., Smith, C. J., Palmer, M. S., Clarke, A. R. and Jefferys, J. G. (1994) Nature, 370, 295. Tobler, I., Gaus, S. E., Deboer, T., Achermann, P., Fischer, M., Rulicke, T., Moser, M., Oesch, B., McBride, P. A. and Manson, J. C. (1996) Nature, 380, 639. Katamine, S., Nishida, N., Sugimoto, T., Noda, T., Sakaguchi, S., Shigematsu, K., Kataoka, Y., Nakatani, A., Hasegawa, S., Moriuchi, R. and Miyamoto, T. (1998) Cell. Mol. Neurobiol., 18, 731. Nazor, K. E., Seward, T. and Telling, G. C. (2007) Biochim. Biophys. Acta, 1772, 645. Brown, D. R., Qin, K., Herms, J. W., Madlung, A., Manson, J., Strome, R., Fraser, P. E., Kruck, T., von Bohlen, A., SchulzSchaeffer, W., Giese, A., Westaway, D. and Kretzschmar, H. (1997) Nature, 390, 684. Wong, B. S., Liu, T., Li, R., Pan, T., Petersen, R. B., Smith, M. A., Gambetti, P., Perry, G., Manson, J. C., Brown, D. R. and Sy, M. S. (2001) J. Neurochem., 76, 565. Brown, D. R., Schulz-Schaeffer, W. J., Schmidt, B. and Kretzschmar, H. A. (1997) Exp. Neurol., 146, 104. Klamt, F., Dal-Pizzol, F., Conte da Frota, M. J., Walz, R., Andrades, M. E., da Silva, E. G., Brentani, R. R., Izquierdo, I. and Fonseca Moreira, J. C. (2001) Free Radic. Biol. Med., 30, 1137. Prusiner, S. B., McKinley, M. P., Bowman, K. A., Bolton, D. C., Bendheim, P. E., Groth, D. F. and Glenner, G. G. (1983) Cell, 35, 349. Prusiner, S. B. (1998) Proc. Natl. Acad. Sci. USA, 95, 13363. Liberski, P. P. (2004) Folia Neuropathol., 42 (Suppl. B), 109. Chesebro, B., Trifilo, M., Race, R., Meade-White, K., Teng, C., LaCasse, R., Raymond, L., Favara, C., Baron, G., Priola, S., Caughey, B., Masliah, E. and Oldstone, M. (2005) Science, 308, 1435. Lasmezas, C. I., Deslys, J. P., Robain, O., Jaegly, A., Beringue, V., Peyrin, J. M., Fournier, J. G., Hauw, J. J., Rossier, J. and Dormont, D. (1997) Science, 275, 402. Race, R., Meade-White, K., Raines, A., Raymond, G. J., Caughey, B. and Chesebro, B. (2002) J. Infect. Dis., 186 (Suppl. 2), S166. Shaked, G. M., Fridlander, G., Meiner, Z., Taraboulos, A. and Gabizon, R. (1999) J. Biol. Chem., 274, 17981. Manson, J. C., Jamieson, E., Baybutt, H., Tuzi, N. L., Barron, R., McConnell, I., Somerville, R., Ironside, J., Will, R., Sy, M. S., Melton, D. W., Hope, J. and Bostock, C. (1999) EMBO J., 18, 6855. Caughey, B., Raymond, G. J., Kocisko, D. A. and Lansbury, P. T., Jr. (1997) J. Virol., 71, 4107. Markovits, P., Dautheville, C., Dormont, D., Dianoux, L. and Latarjet, R. (1983) Acta Neuropathol., 60, 75. Clarke, M. C. and Millson, G. C. (1976) Nature, 261, 144. Rubenstein, R., Carp, R. I. and Callahan, S. M. (1984) J. Gen. Virol., 65 ( Pt 12), 2191. Kocisko, D. A., Come, J. H., Priola, S. A., Chesebro, B., Raymond, G. J., Lansbury, P. T. and Caughey, B. (1994) Nature, 370, 471. Bessen, R. A., Kocisko, D. A., Raymond, G. J., Nandan, S., Lansbury, P. T. and Caughey, B. (1995) Nature, 375, 698.

Protein & Peptide Letters, 2009, Vol. 16, No. 1 [59] [60] [61] [62] [63] [64] [65] [66] [67] [68] [69] [70] [71] [72] [73] [74] [75]

[76] [77] [78] [79] [80] [81] [82] [83] [84] [85] [86] [87] [88] [89] [90] [91] [92] [93]

23

Kocisko, D. A., Priola, S. A., Raymond, G. J., Chesebro, B., Lansbury, P. T., Jr. and Caughey, B. (1995) Proc. Natl. Acad. Sci. USA, 92, 3923. Caughey, B., Kocisko, D. A., Raymond, G. J. and Lansbury, P. T., Jr. (1995) Chem. Biol., 2, 807. Bessen, R. A., Raymond, G. J. and Caughey, B. (1997) J. Biol. Chem., 272, 15227. Saborio, G. P., Soto, C., Kascsak, R. J., Levy, E., Kascsak, R., Harris, D. A. and Frangione, B. (1999) Biochem. Biophys. Res. Commun., 258, 470. Saborio, G. P., Permanne, B. and Soto, C. (2001) Nature, 411, 810. Atarashi, R., Wilham, J. M., Christensen, L., Hughson, A. G., Moore, R. A., Johnson, L. M., Onwubiko, H. A., Priola, S. A. and Caughey, B. (2008) Nat. Methods., 5, 211. Atarashi, R., Moore, R. A., Sim, V. L., Hughson, A. G., Dorward, D. W., Onwubiko, H. A., Priola, S. A. and Caughey, B. (2007) Nat. Methods., 4, 645. Xiong, L. W., Raymond, L. D., Hayes, S. F., Raymond, G. J. and Caughey, B. (2001) J. Neurochem., 79, 669. Silva, J. L., Cordeiro, Y. and Foguel, D. (2006) Biochim. Biophys. Acta, 1764, 443. Torrent, J., Alvarez-Martinez, M. T., Liautard, J. P. and Lange, R. (2006) Biochim. Biophys. Acta, 1764, 546. Jackson, G. S., Hill, A. F., Joseph, C., Hosszu, L., Power, A., Waltho, J. P., Clarke, A. R. and Collinge, J. (1999) Biochim. Biophys. Acta, 1431, 1. Jackson, G. S., Hosszu, L. L., Power, A., Hill, A. F., Kenney, J., Saibil, H., Craven, C. J., Waltho, J. P., Clarke, A. R. and Collinge, J. (1999) Science, 283, 1935. Martins, S. M., Frosoni, D. J., Martinez, A. M., De Felice, F. G. and Ferreira, S. T. (2006) J. Biol. Chem., 281, 26121. Rezaei, H., Choiset, Y., Eghiaian, F., Treguer, E., Mentre, P., Debey, P., Grosclaude, J. and Haertle, T. (2002) J. Mol. Biol., 322, 799. Qin, K., Yang, D. S., Yang, Y., Chishti, M. A., Meng, L. J., Kretzschmar, H. A., Yip, C. M., Fraser, P. E. and Westaway, D. (2000) J. Biol. Chem., 275, 19121. Tsiroulnikov, K., Rezaei, H., Dalgalarrondo, M., Chobert, J. M., Grosclaude, J. and Haertle, T. (2006) Biochim. Biophys. Acta, 1764, 1218. Redecke, L., von Bergen, M., Clos, J., Konarev, P. V., Svergun, D. I., Fittschen, U. E., Broekaert, J. A., Bruns, O., Georgieva, D., Mandelkow, E., Genov, N. and Betzel, C. (2007) J. Struct. Biol., 157, 308. Requena, J. R., Groth, D., Legname, G., Stadtman, E. R., Prusiner, S. B. and Levine, R. L. (2001) Proc. Natl. Acad. Sci. USA, 98, 7170. Lee, S. and Eisenberg, D. (2003) Nat. Struct. Biol., 10, 725. Baskakov, I. V., Legname, G., Prusiner, S. B. and Cohen, F. E. (2001) J. Biol. Chem., 276, 19687. Caughey, B., Raymond, G. J., Ernst, D. and Race, R. E. (1991) J. Virol., 65, 6597. Borchelt, D. R., Taraboulos, A. and Prusiner, S. B. (1992) J. Biol. Chem., 267, 16188. LeVine, H., 3rd (1993) Protein Sci.,, 2, 404. Naiki, H., Higuchi, K., Hosokawa, M. and Takeda, T. (1989) Anal. Biochem., 177, 244. Groenning, M., Norrman, M., Flink, J. M., van de Weert, M., Bukrinsky, J. T., Schluckebier, G. and Frokjaer, S. (2007) J. Struct. Biol., 159, 483. Groenning, M., Olsen, L., van de Weert, M., Flink, J. M., Frokjaer, S. and Jorgensen, F. S. (2007) J. Struct. Biol., 158, 358. Maskevich, A. A., Stsiapura, V. I., Kuzmitsky, V. A., Kuznetsova, I. M., Povarova, O. I., Uversky, V. N. and Turoverov, K. K. (2007) J. Proteome Res., 6, 1392. Azzi, A. (1974) Methods Enzymol., 32, 234. Stryer, L. (1965) J. Mol. Biol., 13, 482. Cohen, F. E., Pan, K. M., Huang, Z., Baldwin, M., Fletterick, R. J. and Prusiner, S. B. (1994) Science, 264, 530. Harper, J. D. and Lansbury, P. T., Jr. (1997) Annu. Rev. Biochem., 66, 385. Baskakov, I. V. (2007) FEBS J., 274, 3756. Aguzzi, A. and Polymenidou, M. (2004) Cell, 116, 313. Govaerts, C., Wille, H., Prusiner, S. B. and Cohen, F. E. (2004) Proc. Natl. Acad. Sci. USA, 101, 8342. Morillas, M., Vanik, D. L. and Surewicz, W. K. (2001) Biochemistry, 40, 6982.

24 Protein & Peptide Letters, 2009, Vol. 16, No. 1 [94] [95] [96] [97] [98] [99] [100]

[101] [102] [103] [104] [105] [106] [107] [108] [109] [110] [111] [112] [113] [114] [115] [116] [117] [118] [119] [120] [121] [122] [123] [124] [125] [126] [127] [128] [129]

Baskakov, I. V., Legname, G., Baldwin, M. A., Prusiner, S. B. and Cohen, F. E. (2002) J. Biol. Chem., 277, 21140. Sokolowski, F., Modler, A. J., Masuch, R., Zirwer, D., Baier, M., Lutsch, G., Moss, D. A., Gast, K. and Naumann, D. (2003) J. Biol. Chem., 278, 40481. Weissmann, C. (1991) Nature, 352, 679. El Moustaine, D., Perrier, V., Smeller, L., Lange, R. and Torrent, J. (2008) FEBS J., 275, 2021. Haass, C. and Selkoe, D. J. (2007) Nat. Rev. Mol. Cell Biol., 8, 101. Bocharova, O. V., Breydo, L., Parfenov, A. S., Salnikov, V. V. and Baskakov, I. V. (2005) J. Mol. Biol., 346, 645. Teplow, D. B., Lazo, N. D., Bitan, G., Bernstein, S., Wyttenbach, T., Bowers, M. T., Baumketner, A., Shea, J. E., Urbanc, B., Cruz, L., Borreguero, J. and Stanley, H. E. (2006) Acc. Chem. Res., 39, 635. Soto, C. and Estrada, L. D. (2008) Arch Neurol, 65, 184. Vendrely, C., Valadie, H., Bednarova, L., Cardin, L., Pasdeloup, M., Cappadoro, J., Bednar, J., Rinaudo, M. and Jamin, M. (2005) Biochim. Biophys. Acta, 1724, 355. Guijarro, J. I., Sunde, M., Jones, J. A., Campbell, I. D. and Dobson, C. M. (1998) Proc. Natl. Acad. Sci. USA, 95, 4224. Knaus, K. J., Morillas, M., Swietnicki, W., Malone, M., Surewicz, W. K. and Yee, V. C. (2001) Nat. Struct. Biol., 8, 770. Kaimann, T., Metzger, S., Kuhlmann, K., Brandt, B., Birkmann, E., Holtje, H. D. and Riesner, D. (2008) J. Mol. Biol., 376, 582. Priola, S. A., Caughey, B., Wehrly, K. and Chesebro, B. (1995) J. Biol. Chem., 270, 3299. Luhrs, T., Zahn, R. and Wuthrich, K. (2006) J. Mol. Biol., 357, 833. Goggin, K., Bissonnette, C., Grenier, C., Volkov, L. and Roucou, X. (2007) J. Neurochem., 102, 1195. Stohr, J., Weinmann, N., Wille, H., Kaimann, T., Nagel-Steger, L., Birkmann, E., Panza, G., Prusiner, S. B., Eigen, M. and Riesner, D. (2008) Proc. Natl. Acad. Sci. USA, 105, 2409. Makin, O. S. and Serpell, L. C. (2002) Biochem. Soc. Trans., 30, 521. Nelson, R., Sawaya, M. R., Balbirnie, M., Madsen, A. O., Riekel, C., Grothe, R. and Eisenberg, D. (2005) Nature, 435, 773. Shewmaker, F., Wickner, R. B. and Tycko, R. (2006) Proc. Natl. Acad. Sci. USA, 103, 19754. Torok, M., Milton, S., Kayed, R., Wu, P., McIntire, T., Glabe, C. G. and Langen, R. (2002) J. Biol. Chem., 277, 40810. Chen, M., Margittai, M., Chen, J. and Langen, R. (2007) J. Biol. Chem., 282, 24970. Margittai, M. and Langen, R. (2004) Proc. Natl. Acad. Sci. USA, 101, 10278. Sun, Y., Makarava, N., Lee, C. I., Laksanalamai, P., Robb, F. T. and Baskakov, I. V. (2008) J. Mol. Biol., 376, 1155. Cobb, N. J., Sonnichsen, F. D., McHaourab, H. and Surewicz, W. K. (2007) Proc. Natl. Acad. Sci. USA, 104, 18946. Lu, X., Wintrode, P. L. and Surewicz, W. K. (2007) Proc. Natl. Acad. Sci. USA, 104, 1510. Novitskaya, V., Makarava, N., Bellon, A., Bocharova, O. V., Bronstein, I. B., Williamson, R. A. and Baskakov, I. V. (2006) J. Biol. Chem., 281, 15536. DeMarco, M. L. and Daggett, V. (2004) Proc. Natl. Acad. Sci. USA, 101, 2293. Dima, R. I. and Thirumalai, D. (2002) Biophys. J., 83, 1268. Watzlawik, J., Skora, L., Frense, D., Griesinger, C., Zweckstetter, M., Schulz-Schaeffer, W. J. and Kramer, M. L. (2006) J. Biol. Chem., 281, 30242. Yu, S., Yin, S., Li, C., Wong, P., Chang, B., Xiao, F., Kang, S. C., Yan, H., Xiao, G., Tien, P. and Sy, M. S. (2007) Biochem. J., 403, 343. Liu, A., Riek, R., Zahn, R., Hornemann, S., Glockshuber, R. and Wuthrich, K. (1999) Biopolymers, 51, 145. Speare, J. O., Rush, T. S. III, Bloom, M. E. and Caughey, B. (2003) J. Biol. Chem., 278, 12522. Ziegler, J., Sticht, H., Marx, U. C., Muller, W., Rosch, P. and Schwarzinger, S. (2003) J. Biol. Chem., 278, 50175. Morrissey, M. P. and Shakhnovich, E. I. (1999) Proc. Natl. Acad. Sci. USA, 96, 11293. Dima, R. I. and Thirumalai, D. (2004) Proc. Natl. Acad. Sci. USA, 101, 15335. Fitzmaurice, T. J., Burke, D. F., Hopkins, L., Yang, S., Yu, S., Sy, M. S., Thackray, A. M. and Bujdoso, R. (2008) Biochem. J., 409, 367.

Fontaine and Brown [130] [131] [132] [133] [134] [135]

[136] [137] [138] [139] [140] [141] [142] [143] [144] [145] [146] [147] [148] [149] [150] [151] [152] [153] [154] [155] [156] [157] [158] [159] [160] [161] [162] [163] [164] [165] [166]

Frankenfield, K. N., Powers, E. T. and Kelly, J. W. (2005) Protein Sci.,, 14, 2154. Mead, S. (2006) Eur. J. Hum. Genet., 14, 273. Collinge, J., Sidle, K. C., Meads, J., Ironside, J. and Hill, A. F. (1996) Nature, 383, 685. Collinge, J., Palmer, M. S. and Dryden, A. J. (1991) Lancet, 337, 1441. Zeidler, M., Stewart, G., Cousens, S. N., Estibeiro, K. and Will, R. G. (1997) Lancet, 350, 668. Hill, A. F., Butterworth, R. J., Joiner, S., Jackson, G., Rossor, M. N., Thomas, D. J., Frosh, A., Tolley, N., Bell, J. E., Spencer, M., King, A., Al-Sarraj, S., Ironside, J. W., Lantos, P. L. and Collinge, J. (1999) Lancet, 353, 183. Lee, H. S., Brown, P., Cervenakova, L., Garruto, R. M., Alpers, M. P., Gajdusek, D. C. and Goldfarb, L. G. (2001) J. Infect. Dis., 183, 192. Mead, S., Stumpf, M. P., Whitfield, J., Beck, J. A., Poulter, M., Campbell, T., Uphill, J. B., Goldstein, D., Alpers, M., Fisher, E. M. and Collinge, J. (2003) Science, 300, 640. Hosszu, L. L., Jackson, G. S., Trevitt, C. R., Jones, S., Batchelor, M., Bhelt, D., Prodromidou, K., Clarke, A. R., Waltho, J. P. and Collinge, J. (2004) J. Biol. Chem., 279, 28515. Wong, B. S., Clive, C., Haswell, S. J., Williamson, R. A., Burton, D. R., Gambetti, P., Sy, M. S., Jones, I. M. and Brown, D. R. (2000) Biochem. Biophys. Res. Commun., 269, 726. Lewis, P. A., Tattum, M. H., Jones, S., Bhelt, D., Batchelor, M., Clarke, A. R., Collinge, J. and Jackson, G. S. (2006) J. Gen. Virol., 87, 2443. Tahiri-Alaoui, A., Sim, V. L., Caughey, B. and James, W. (2006) J. Biol. Chem., 281, 34171. Tahiri-Alaoui, A., Gill, A. C., Disterer, P. and James, W. (2004) J. Biol. Chem., 279, 31390. Tahiri-Alaoui, A. and James, W. (2005) Protein Sci., 14, 942. Baskakov, I., Disterer, P., Breydo, L., Shaw, M., Gill, A., James, W. and Tahiri-Alaoui, A. (2005) FEBS Lett., 579, 2589. Liemann, S. and Glockshuber, R. (1999) Biochemistry, 38, 3258. Pham, N., Yin, S., Yu, S., Wong, P., Kang, S. C., Li, C. and Sy, M. S. (2008) Biochem. Biophys. Res. Commun., 368, 875. Shamsir, M. S. and Dalby, A. R. (2005) Proteins, 59, 275. Apetri, A. C., Vanik, D. L. and Surewicz, W. K. (2005) Biochemistry, 44, 15880. Vanik, D. L. and Surewicz, W. K. (2002) J. Biol. Chem., 277, 49065. Apetri, A. C., Surewicz, K. and Surewicz, W. K. (2004) J. Biol. Chem., 279, 18008. Apetri, A. C. and Surewicz, W. K. (2002) J. Biol. Chem., 277, 44589. Jones, E. M., Surewicz, K. and Surewicz, W. K. (2006) J. Biol. Chem., 281, 8190. Singh, N., Zanusso, G., Chen, S. G., Fujioka, H., Richardson, S., Gambetti, P. and Petersen, R. B. (1997) J. Biol. Chem., 272, 28461. Moore, R. A., Hayes, S. F., Fischer, E. R. and Priola, S. A. (2007) Biochemistry, 46, 7079. Tank, E. M., Harris, D. A., Desai, A. A. and True, H. L. (2007) Mol. Cell. Biol., 27, 5445. Kalastavadi, T. and True, H. L. (2008) BMC Biochem., 9, 7. Priola, S. A. and Chesebro, B. (1998) J. Biol. Chem., 273, 11980. Li, R., Liu, T., Wong, B. S., Pan, T., Morillas, M., Swietnicki, W., O'Rourke, K., Gambetti, P., Surewicz, W. K. and Sy, M. S. (2000) J. Mol. Biol., 301, 567. Zahn, R. (2003) J. Mol. Biol., 334, 477. Bossers, A., de Vries, R. and Smits, M. A. (2000) J. Virol., 74, 1407. Bossers, A., Belt, P., Raymond, G. J., Caughey, B., de Vries, R. and Smits, M. A. (1997) Proc. Natl. Acad. Sci. USA, 94, 4931. Yang, S., Thackray, A. M., Fitzmaurice, T. J. and Bujdoso, R. (2008) Biochim. Biophys. Acta, 1784, 683. Collinge, J. and Clarke, A. R. (2007) Science, 318, 930. Viles, J. H., Cohen, F. E., Prusiner, S. B., Goodin, D. B., Wright, P. E. and Dyson, H. J. (1999) Proc. Natl. Acad. Sci. USA, 96, 2042. Brown, D. R., Hafiz, F., Glasssmith, L. L., Wong, B. S., Jones, I. M., Clive, C. and Haswell, S. J. (2000) EMBO J., 19, 1180. Aronoff-Spencer, E., Burns, C. S., Avdievich, N. I., Gerfen, G. J., Peisach, J., Antholine, W. E., Ball, H. L., Cohen, F. E., Prusiner, S. B. and Millhauser, G. L. (2000) Biochemistry, 39, 13760.

Mechanisms of Prion Protein Aggregation [167] [168] [169] [170] [171] [172] [173] [174] [175] [176] [177] [178] [179] [180] [181] [182] [183] [184] [185] [186]

[187] [188] [189] [190] [191] [192] [193] [194] [195] [196] [197] [198] [199] [200] [201] [202] [203]

Jackson, G. S., Murray, I., Hosszu, L. L., Gibbs, N., Waltho, J. P., Clarke, A. R. and Collinge, J. (2001) Proc. Natl. Acad. Sci. USA, 98, 8531. McKenzie, D., Bartz, J., Mirwald, J., Olander, D., Marsh, R. and Aiken, J. (1998) J. Biol. Chem., 273, 25545. Quaglio, E., Chiesa, R. and Harris, D. A. (2001) J. Biol. Chem., 276, 11432. Wadsworth, J. D., Hill, A. F., Joiner, S., Jackson, G. S., Clarke, A. R. and Collinge, J. (1999) Nat. Cell. Biol., 1, 55. Stockel, J., Safar, J., Wallace, A. C., Cohen, F. E. and Prusiner, S. B. (1998) Biochemistry, 37, 7185. Wong, B. S., Chen, S. G., Colucci, M., Xie, Z., Pan, T., Liu, T., Li, R., Gambetti, P., Sy, M. S. and Brown, D. R. (2001) J. Neurochem., 78, 1400. Nishida, Y., Sodeyama, N., Toru, Y., Toru, S., Kitamoto, T. and Mizusawa, H. (2004) Neurology, 63, 1978. Jones, C. E., Abdelraheim, S. R., Brown, D. R. and Viles, J. H. (2004) J. Biol. Chem., 279, 32018. Liu, M., Yu, S., Yang, J., Yin, X. and Zhao, D. (2007) Mol. Cell. Biochem., 294, 197. Wong, E., Thackray, A. M. and Bujdoso, R. (2004) Biochem. J., 380, 273. Thackray, A. M., Yang, S., Wong, E., Fitzmaurice, T. J., MorganWarren, R. J. and Bujdoso, R. (2004) Biochem. J., 381, 221. Giese, A., Levin, J., Bertsch, U. and Kretzschmar, H. (2004) Biochem. Biophys. Res. Commun., 320, 1240. Bocharova, O. V., Breydo, L., Salnikov, V. V. and Baskakov, I. V. (2005) Biochemistry, 44, 6776. Ricchelli, F., Buggio, R., Drago, D., Salmona, M., Forloni, G., Negro, A., Tognon, G. and Zatta, P. (2006) Biochemistry, 45, 6724. Liu, M. L., Li, Y. X., Zhou, X. M. and Zhao, D. M. (2008) J. Biochem., 143, 333. Orem, N. R., Geoghegan, J. C., Deleault, N. R., Kascsak, R. and Supattapone, S. (2006) J. Neurochem., 96, 1409. Rezaei, H., Eghiaian, F., Perez, J., Doublet, B., Choiset, Y., Haertle, T. and Grosclaude, J. (2005) J. Mol. Biol., 347, 665. Shiraishi, N., Inai, Y., Bi, W. and Nishikimi, M. (2005) Biochem. J., 387, 247. Tsiroulnikov, K., Chobert, J. M. and Haertle, T. (2006) FEBS J., 273, 1959. Jobling, M. F., Huang, X., Stewart, L. R., Barnham, K. J., Curtain, C., Volitakis, I., Perugini, M., White, A. R., Cherny, R. A., Masters, C. L., Barrow, C. J., Collins, S. J., Bush, A. I. and Cappai, R. (2001) Biochemistry, 40, 8073. Haigh, C. L., Edwards, K. and Brown, D. R. (2005) Mol. Cell. Neurosci., 30, 186. Brown, L. R. and Harris, D. A. (2003) J. Neurochem., 87, 353. Perera, W. S. and Hooper, N. M. (2001) Curr. Biol., 11, 519. Pauly, P. C. and Harris, D. A. (1998) J. Biol. Chem., 273, 33107. Brazier, M. W., Davies, P., Player, E., Marken, F., Viles, J. H. and Brown, D. R. (2008) J. Biol. Chem., 283, 12831. Abdelraheim, S. R., Kralovicova, S. and Brown, D. R. (2006) Int. J. Biochem. Cell Biol., 38, 1429. Lekishvili, T., Sassoon, J., Thompsett, A. R., Green, A., Ironside, J. W. and Brown, D. R. (2004) Exp. Neurol., 190, 233. Kim, N. H., Choi, J. K., Jeong, B. H., Kim, J. I., Kwon, M. S., Carp, R. I. and Kim, Y. S. (2005) FASEB J., 19, 783. Davies, P. and Brown, D. R. (2008) Biochem. J., 410, 237. Dong, J., Canfield, J. M., Mehta, A. K., Shokes, J. E., Tian, B., Childers, W. S., Simmons, J. A., Mao, Z., Scott, R. A., Warncke, K. and Lynn, D. G. (2007) Proc. Natl. Acad. Sci. USA, 104, 13313. Wong, C., Xiong, L. W., Horiuchi, M., Raymond, L., Wehrly, K., Chesebro, B. and Caughey, B. (2001) EMBO J., 20, 377. Gonzalez-Iglesias, R., Pajares, M. A., Ocal, C., Espinosa, J. C., Oesch, B. and Gasset, M. (2002) J. Mol. Biol., 319, 527. Yin, S., Pham, N., Yu, S., Li, C., Wong, P., Chang, B., Kang, S. C., Biasini, E., Tien, P., Harris, D. A. and Sy, M. S. (2007) Proc. Natl. Acad. Sci. USA, 104, 7546. Deleault, N. R., Geoghegan, J. C., Nishina, K., Kascsak, R., Williamson, R. A. and Supattapone, S. (2005) J. Biol. Chem., 280, 26873. Boshuizen, R. S., Morbin, M., Mazzoleni, G., Tagliavini, F., Meloen, R. H. and Langedijk, J. P. (2007) Amyloid, 14, 205. Perez, M., Wandosell, F., Colaco, C. and Avila, J. (1998) Biochem. J., 335 ( Pt 2), 369. Warner, R. G., Hundt, C., Weiss, S. and Turnbull, J. E. (2002) J. Biol. Chem., 277, 18421.

Protein & Peptide Letters, 2009, Vol. 16, No. 1 [204] [205] [206] [207] [208] [209] [210] [211] [212] [213] [214] [215] [216] [217]

[218] [219] [220] [221] [222] [223] [224] [225] [226] [227] [228] [229] [230] [231] [232] [233] [234] [235] [236] [237] [238] [239] [240]

25

Pan, T., Wong, B. S., Liu, T., Li, R., Petersen, R. B. and Sy, M. S. (2002) Biochem. J., 368, 81. Hijazi, N., Kariv-Inbal, Z., Gasset, M. and Gabizon, R. (2005) J. Biol. Chem., 280, 17057. Horonchik, L., Tzaban, S., Ben-Zaken, O., Yedidia, Y., Rouvinski, A., Papy-Garcia, D., Barritault, D., Vlodavsky, I. and Taraboulos, A. (2005) J. Biol. Chem., 280, 17062. Cohlberg, J. A., Li, J., Uversky, V. N. and Fink, A. L. (2002) Biochemistry, 41, 1502. Yamin, G., Munishkina, L. A., Karymov, M. A., Lyubchenko, Y. L., Uversky, V. N. and Fink, A. L. (2005) Biochemistry, 44, 9096. McLaurin, J., Franklin, T., Kuhns, W. J. and Fraser, P. E. (1999) Amyloid, 6, 233. Caughey, B., Ernst, D. and Race, R. E. (1993) J. Virol., 67, 6270. Caughey, B. and Race, R. E. (1992) J. Neurochem., 59, 768. Caspi, S., Halimi, M., Yanai, A., Sasson, S. B., Taraboulos, A. and Gabizon, R. (1998) J. Biol. Chem., 273, 3484. Rudyk, H., Vasiljevic, S., Hennion, R. M., Birkett, C. R., Hope, J. and Gilbert, I. H. (2000) J. Gen. Virol., 81, 1155. Caughey, B. and Raymond, G. J. (1993) J. Virol., 67, 643. Ingrosso, L., Ladogana, A. and Pocchiari, M. (1995) J. Virol., 69, 506. Beringue, V., Adjou, K. T., Lamoury, F., Maignien, T., Deslys, J. P., Race, R. and Dormont, D. (2000) J. Virol., 74, 5432. Poli, G., Martino, P. A., Villa, S., Carcassola, G., Giannino, M. L., Dall'Ara, P., Pollera, C., Iussich, S., Tranquillo, V. M., Bareggi, S., Mantegazza, P. and Ponti, W. (2004) Arzneimittelforschung, 54, 406. Frid, P., Anisimov, S. V. and Popovic, N. (2007) Brain Res. Rev., 53, 135. Webb, S., Lekishvili, T., Loeschner, C., Sellarajah, S., Prelli, F., Wisniewski, T., Gilbert, I. H. and Brown, D. R. (2007) J. Virol., 81, 10729. Lorenzo, A. and Yankner, B. A. (1994) Proc. Natl. Acad. Sci. USA, 91, 12243. Podlisny, M. B., Walsh, D. M., Amarante, P., Ostaszewski, B. L., Stimson, E. R., Maggio, J. E., Teplow, D. B. and Selkoe, D. J. (1998) Biochemistry, 37, 3602. Klajnert, B., Cortijo-Arellano, M., Cladera, J., Majoral, J. P., Caminade, A. M. and Bryszewska, M. (2007) Biochem. Biophys. Res. Commun., 364, 20. Klajnert, B., Cortijo-Arellano, M., Cladera, J. and Bryszewska, M. (2006) Biochem. Biophys. Res. Commun., 345, 21. Supattapone, S., Nguyen, H. O., Cohen, F. E., Prusiner, S. B. and Scott, M. R. (1999) Proc. Natl. Acad. Sci. USA, 96, 14529. Caughey, B., Raymond, L. D., Raymond, G. J., Maxson, L., Silveira, J. and Baron, G. S. (2003) J. Virol., 77, 5499. Pandey, N., Strider, J., Nolan, W. C., Yan, S. X. and Galvin, J. E. (2008) Acta Neuropathol., 115, 479. Reinke, A. A. and Gestwicki, J. E. (2007) Chem. Biol. Drug Des., 70, 206. Hafner-Bratkovic, I., Gaspersic, J., Smid, L. M., Bresjanac, M. and Jerala, R. (2008) J. Neurochem., 104, 1553. Porat, Y., Abramowitz, A. and Gazit, E. (2006) Chem. Biol. Drug Des., 67, 27. Arbel, M., Lavie, V. and Solomon, B. (2003) J. Neuroimmunol., 144, 38. Alper, T., Haig, D. A. and Clarke, M. C. (1966) Biochem. Biophys. Res. Commun., 22, 278. Bellinger-Kawahara, C. G., Kempner, E., Groth, D., Gabizon, R. and Prusiner, S. B. (1988) Virology, 164, 537. Gabizon, R., McKinley, M. P. and Prusiner, S. B. (1987) Proc. Natl. Acad. Sci. USA, 84, 4017. Caughey, B. and Lansbury, P. T. (2003) Annu. Rev. Neurosci., 26, 267. Tzaban, S., Friedlander, G., Schonberger, O., Horonchik, L., Yedidia, Y., Shaked, G., Gabizon, R. and Taraboulos, A. (2002) Biochemistry, 41, 12868. Silveira, J. R., Raymond, G. J., Hughson, A. G., Race, R. E., Sim, V. L., Hayes, S. F. and Caughey, B. (2005) Nature, 437, 257. Lu, B. Y. and Chang, J. Y. (2002) Biochem. J., 364, 81. Piccardo, P., Manson, J. C., King, D., Ghetti, B. and Barron, R. M. (2007) Proc. Natl. Acad. Sci. USA, 104, 4712. Forloni, G., Angeretti, N., Chiesa, R., Monzani, E., Salmona, M., Bugiani, O. and Tagliavini, F. (1993) Nature, 362, 543. Brown, D. R. (2000) Mol. Cell. Neurosci., 15, 66.

26 Protein & Peptide Letters, 2009, Vol. 16, No. 1 [241] [242] [243] [244] [245] [246] [247] [248] [249]

[250] [251]

[252] [253] [254] [255] [256] [257] [258] [259]

[260] [261]

Fontaine and Brown

Daniels, M., Cereghetti, G. M. and Brown, D. R. (2001) Eur. J. Biochem., 268, 6155. Dear, D. V., Young, D. S., Kazlauskaite, J., Meersman, F., Oxley, D., Webster, J., Pinheiro, T. J., Gill, A. C., Bronstein, I. and Lowe, C. R. (2007) Biochim. Biophys. Acta, 1774, 792. Tanaka, M., Collins, S. R., Toyama, B. H. and Weissman, J. S. (2006) Nature, 442, 585. Lee, K. S. and Caughey, B. (2007) Proc. Natl. Acad. Sci. USA, 104, 9551. Widenbrant, M. J., Rajadas, J., Sutardja, C. and Fuller, G. G. (2006) Biophys. J., 91, 4071. Kazlauskaite, J., Young, A., Gardner, C. E., Macpherson, J. V., Venien-Bryan, C. and Pinheiro, T. J. (2005) Biochem. Biophys. Res. Commun., 328, 292. Novitskaya, V., Bocharova, O. V., Bronstein, I. and Baskakov, I. V. (2006) J. Biol. Chem., 281, 13828. Villa, V., Corsaro, A., Thellung, S., Paludi, D., Chiovitti, K., Venezia, V., Nizzari, M., Russo, C., Schettini, G., Aceto, A. and Florio, T. (2006) Ann. N.Y. Acad. Sci., 1090, 276. Corsaro, A., Paludi, D., Villa, V., D'Arrigo, C., Chiovitti, K., Thellung, S., Russo, C., Di Cola, D., Ballerini, P., Patrone, E., Schettini, G., Aceto, A. and Florio, T. (2006) Int. J. Immunopathol. Pharmacol., 19, 339. Chiovitti, K., Corsaro, A., Thellung, S., Villa, V., Paludi, D., D'Arrigo, C., Russo, C., Perico, A., Ianieri, A., Di Cola, D., Vergara, A., Aceto, A. and Florio, T. (2007) J. Neurochem., 103, 2597. Simoneau, S., Rezaei, H., Sales, N., Kaiser-Schulz, G., LefebvreRoque, M., Vidal, C., Fournier, J. G., Comte, J., Wopfner, F., Grosclaude, J., Schatzl, H. and Lasmezas, C. I. (2007) PLoS Pathog., 3, e125. Novitskaya, V., Makarava, N., Sylvester, I., Bronstein, I. B. and Baskakov, I. V. (2007) J. Neurochem., 102, 398. Jeffrey, M., Halliday, W. G., Bell, J., Johnston, A. R., MacLeod, N. K., Ingham, C., Sayers, A. R., Brown, D. A. and Fraser, J. R. (2000) Neuropathol. Appl. Neurobiol., 26, 41. Brandner, S., Raeber, A., Sailer, A., Blattler, T., Fischer, M., Weissmann, C. and Aguzzi, A. (1996) Proc. Natl. Acad. Sci. USA, 93, 13148. Mironov, A. Jr., Latawiec, D., Wille, H., Bouzamondo-Bernstein, E., Legname, G., Williamson, R. A., Burton, D., DeArmond, S. J., Prusiner, S. B. and Peters, P. J. (2003) J. Neurosci., 23, 7183. Pieri, L., Bucciantini, M., Nosi, D., Formigli, L., Savistchenko, J., Melki, R. and Stefani, M. (2006) J. Biol. Chem., 281, 15337. Vieira, M. N., Forny-Germano, L., Saraiva, L. M., Sebollela, A., Martinez, A. M., Houzel, J. C., De Felice, F. G. and Ferreira, S. T. (2007) J. Neurochem., 103, 736. Kayed, R., Head, E., Thompson, J. L., McIntire, T. M., Milton, S. C., Cotman, C. W. and Glabe, C. G. (2003) Science, 300, 486. Kayed, R., Head, E., Sarsoza, F., Saing, T., Cotman, C. W., Necula, M., Margol, L., Wu, J., Breydo, L., Thompson, J. L., Rasool, S., Gurlo, T., Butler, P. and Glabe, C. G. (2007) Mol. Neurodegener., 2, 18. Schatzl, H. M., Laszlo, L., Holtzman, D. M., Tatzelt, J., DeArmond, S. J., Weiner, R. I., Mobley, W. C. and Prusiner, S. B. (1997) J. Virol., 71, 8821. Solforosi, L., Criado, J. R., McGavern, D. B., Wirz, S., SanchezAlavez, M., Sugama, S., DeGiorgio, L. A., Volpe, B. T., Wiseman, E., Abalos, G., Masliah, E., Gilden, D., Oldstone, M. B., Conti, B. and Williamson, R. A. (2004) Science, 303, 1514.

Received: April 28, 2008

Revised: June 13, 2008

Accepted: June 27, 2008

[262] [263] [264] [265] [266] [267] [268] [269] [270] [271] [272] [273] [274] [275]

[276] [277]

[278] [279] [280] [281] [282] [283] [284] [285] [286] [287]

Demuro, A., Mina, E., Kayed, R., Milton, S. C., Parker, I. and Glabe, C. G. (2005) J. Biol. Chem., 280, 17294. Hetz, C. A. and Soto, C. (2006) Curr. Mol. Med., 6, 37. Behl, C., Davis, J. B., Lesley, R. and Schubert, D. (1994) Cell, 77, 817. Hsu, L. J., Sagara, Y., Arroyo, A., Rockenstein, E., Sisk, A., Mallory, M., Wong, J., Takenouchi, T., Hashimoto, M. and Masliah, E. (2000) Am. J. Pathol., 157, 401. Breusing, N. and Grune, T. (2008) Biol. Chem., 389, 203. Nunomura, A., Moreira, P. I., Takeda, A., Smith, M. A. and Perry, G. (2007) Curr. Med. Chem., 14, 2968. Bennett, E. J., Bence, N. F., Jayakumar, R. and Kopito, R. R. (2005) Mol. Cell, 17, 351. Dahlmann, B. (2007) BMC Biochem., 8 (Suppl 1), S3. Carrard, G., Bulteau, A. L., Petropoulos, I. and Friguet, B. (2002) Int. J. Biochem. Cell Biol., 34, 1461. Verhoef, L. G., Lindsten, K., Masucci, M. G. and Dantuma, N. P. (2002) Hum. Mol. Genet., 11, 2689. Yedidia, Y., Horonchik, L., Tzaban, S., Yanai, A. and Taraboulos, A. (2001) EMBO J., 20, 5383. Ma, J. and Lindquist, S. (2001) Proc. Natl. Acad. Sci. USA, 98, 14955. Kristiansen, M., Messenger, M. J., Klohn, P. C., Brandner, S., Wadsworth, J. D., Collinge, J. and Tabrizi, S. J. (2005) J. Biol. Chem., 280, 38851. Gervais, F. G., Singaraja, R., Xanthoudakis, S., Gutekunst, C. A., Leavitt, B. R., Metzler, M., Hackam, A. S., Tam, J., Vaillancourt, J. P., Houtzager, V., Rasper, D. M., Roy, S., Hayden, M. R. and Nicholson, D. W. (2002) Nat. Cell. Biol., 4, 95. Lu, D. C., Shaked, G. M., Masliah, E., Bredesen, D. E. and Koo, E. H. (2003) Ann. Neurol., 54, 781. Kristiansen, M., Deriziotis, P., Dimcheff, D. E., Jackson, G. S., Ovaa, H., Naumann, H., Clarke, A. R., van Leeuwen, F. W., Menendez-Benito, V., Dantuma, N. P., Portis, J. L., Collinge, J. and Tabrizi, S. J. (2007) Mol. Cell, 26, 175. Cleary, J. P., Walsh, D. M., Hofmeister, J. J., Shankar, G. M., Kuskowski, M. A., Selkoe, D. J. and Ashe, K. H. (2005) Nat. Neurosci., 8, 79. Klyubin, I., Walsh, D. M., Lemere, C. A., Cullen, W. K., Shankar, G. M., Betts, V., Spooner, E. T., Jiang, L., Anwyl, R., Selkoe, D. J. and Rowan, M. J. (2005) Nat. Med., 11, 556. Lesne, S., Kotilinek, L. and Ashe, K. H. (2008) Neuroscience, 151, 745. Ferreira, S. T., Vieira, M. N. and De Felice, F. G. (2007) IUBMB Life, 59, 332. Legname, G., Baskakov, I. V., Nguyen, H. O., Riesner, D., Cohen, F. E., DeArmond, S. J. and Prusiner, S. B. (2004) Science, 305, 673. Bieschke, J., Weber, P., Sarafoff, N., Beekes, M., Giese, A. and Kretzschmar, H. (2004) Proc. Natl. Acad. Sci. USA, 101, 12207. Saa, P., Castilla, J. and Soto, C. (2006) J. Biol. Chem., 281, 35245. Weber, P., Reznicek, L., Mitteregger, G., Kretzschmar, H. and Giese, A. (2008) Biochem. Biophys. Res. Commun., 369, 924. Weber, P., Giese, A., Piening, N., Mitteregger, G., Thomzig, A., Beekes, M. and Kretzschmar, H. A. (2007) Vet. Microbiol., 123, 346. Deleault, N. R., Harris, B. T., Rees, J. R. and Supattapone, S. (2007) Proc. Natl. Acad. Sci. USA, 104, 9741.