Fine Tuning of Microscopic Properties in Two-Component Zwitterionic ...

5 downloads 0 Views 38KB Size Report
Feb 21, 2018 - Anionic Lipid Bilayers: Determinant Role of H-Bonding. Roman G. ... termines the overall bilayer skeleton, important contribution is made by H-.
Wednesday, February 21, 2018 2981-Pos Board B189 Fine Tuning of Microscopic Properties in Two-Component ZwitterionicAnionic Lipid Bilayers: Determinant Role of H-Bonding Roman G. Efremov1,2, Darya V. Pyrkova1, Nikolay A. Krylov1,3. 1 Lab. of Biomolecular Modeling, Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russian Federation, 2National Research University Higher School of Economics, Moscow, Russian Federation, 3Joint Supercomputer Center, Russian Academy of Sciences, Moscow, Russian Federation. Structure, dynamics, and functioning of hydrated lipid bilayers - model cell membranes - are governed by a thin balance of intermolecular interactions between constituents of these systems. Besides the hydrophobic effect, which determines the overall bilayer skeleton, important contribution is made by Hbonds between lipids, water, and ions. This determines crucial phenomena in cell membranes: dynamic clustering, hydration, fine tuning of microscopic physico-chemical properties, which permit fast adaptation of membranes to external agents (e.g., proteins). Characteristics of H-bonds (strength, spatial location, etc.) dramatically depend on local polarity properties of water-lipid environment. Here, we calculated free energies of H-bonded complexes between lipids and water in explicit solvents of different polarity (water, methanol, chloroform) mimicking membrane environment at different depth. The strongest H-bonds were observed in nonpolar environment, although the overall bilayer organization imposes serious limitations on the distribution of various types of H-bonds over hydrophobic/hydrophilic regions (corresponding to dielectric media with low and high permeability). This creates a delicate balance, which determines a unique H-bonding pattern for each particular lipid bilayer. This was confirmed via atomistic molecular dynamics (MD) of several hydrated lipid bilayers. Understanding of the factors regulating H-bonding propensities in such systems is indispensable for rational design of new membranelike materials with predefined properties. One example - an artificial lipid with engineered hydroxyl group - is studied via MD simulations. It is shown that such lipids can induce significant changes of key characteristics of model membranes. This opens new avenues in goal-oriented design of artificial membranes with engineered properties. Acknowledgements: Russian Science Foundation (14-50-00131), Russian Foundation for Basic Research (16-04-00578), RAS MCB Program, Supercomputer Center ‘‘Polytechnical’’ (St. Petersburg Polytechnic University), Joint Supercomputer Center of RAS (Moscow). 2982-Pos Board B190 Shape Transformation of Biomembrane Induced by Banana-Shaped Protein Rods Hiroshi Noguchi. Institute for Solid State Physics, University of Tokyo, Kashiwa, Japan. In living cells, morphology of biomembranes is regulated by various proteins. Many of these proteins contain a banana-shaped binding module called BAR (Bin-Amphiphysin-Rvs) domain. We have studied how anisotropic spontaneous curvatures of banana-shaped protein rod induce effective interaction between the proteins and change membrane shapes by using implicit-solvent meshless membrane simulations [1-6]. The self-assembly of the rods is divided to two directional assemblies at the low rod density [1] and polyhedral and high-genus vesicles are formed at the high density [2,3]. A small spontaneous curvature perpendicular to the rod can remarkably alter the tubulation dynamics at high rod density whereas minor effects are only obtained at low density [4]. Two types of the protein rods with opposite rod curvatures cooperatively induce straight bumps and stripe structures [5]. The addition of small membrane inclusions with isotropic spontaneous curvature accelerates or suppresses the tabulation depending on their curvatures [6]. [1] H. Noguchi, EPL 108, 48001 (2014). [2] H. Noguchi, J. Chem. Phys. 143, 243109 (2015). [3] H. Noguchi, Phys. Rev. E 93, 052404 (2016). [4] H. Noguchi, Sci. Rep. 6, 20935 (2016). [5] H. Noguchi and J.-B. Fournier, Soft Matter 13, 4099 (2017). [6] H. Noguchi, Soft Matter (2017) DOI: 10.1039/C7SM01375B. 2983-Pos Board B191 Cholesterol Chemical Potential in Mixed Phosphatidylcholine/Cholesterol Bilayer: Model Predictions and Computer Simulations Nihit Pokhrel, Lutz Maibaum. Chemistry, University of Washington, Seattle, WA, USA. Cholesterol plays a vital role in maintaining the structure of cellular membranes by inducing order and increasing packing. There are multiple competing models that aim to describe the structure of cholesterol-containing phospholipid bilayers, and these models make specific predictions for the concentration dependence of the cholesterol chemical potential. In this work, we systematically study four phosphatidylcholine (PC) lipids with different degrees of unsaturation to investigate which of these models best describes the bilayer

601a

behavior. We use coarse-grained molecular dynamics simulations together with replica exchange umbrella sampling to calculate the transfer free energy of one cholesterol molecule from the bilayer to bulk water, from which we infer the chemical potential. Our results demonstrate the sensitivity of the chemical potential to the degree of PC tail unsaturation and show that cholesterol has the greatest affinity to saturated PC lipids. Contrary to recent experiments and the conceptual models, our results indicate that the chemical potential increases linearly with increasing cholesterol concentration for all lipid types, suggesting the absence of critical cholesterol concentrations at which the bilayer organization changes dramatically. The increase of the chemical potential with cholesterol content also suggests that cholesterol prefers bilayers with lower cholesterol concentration. 2984-Pos Board B192 Multicomponent Vesicle Membranes: Influence of Material Properties David Salac, Prerna Gera. Mechanical and Aerospace Engineering, University at Buffalo, Buffalo, NY, USA. It is well known that the material properties of multicomponent lipid membranes influence of the dynamics of vesicles. In this work computational tools are used to systematically explore the influence of variable membrane properties, such as bending rigidity, spontaneous curvature, and domain line tension, and fluid properties such as increased vesicle viscosity on the dynamics of deflated three-dimensional vesicles. In addition to reproducing various experimental equilibrium results, the results demonstrate rich behaviour when exposed to externally driven fluid flow and external fields. 2985-Pos Board B193 Diffusive Modes of Archaea Bolalipid Membrane Sergei I. Mukhin, Daria Makitruk, Daniyar Gabdullin. Theoretical Physics and Quantum Technologies, Moscow Institute for Steel and Alloys, Moscow, Russian Federation. One of the distinctions of archaea cell is bolalipid membrane. A feature of the bolalipid membrane is the presence of intrinsically multicomponent content. Bolalipid molecules can exist in two major configurations: integral shaped (Oforms) and hairpin shaped (U-forms). The U-forms surrounded by the Oforms cause local curvature of the membrane. Ability of the U-shapes to move inside the bolalipid layer and dependence of their potential energy on the local curvature of the membrane cause lateral diffusive flaws of U-forms under the membrane’s bending fluctuations. For a theoretical calculation of the bending modes of bolalipid membrane with small concentration of Uforms we take the energy functional of isotropic elastic thin plate with dynamic nonzero local spontaneous curvature J0 proportional to the local concentration of U-forms. Motion of U-forms is described by Fick’s laws in the presence of dynamic potential field effectively created by the membrane’s local bending fluctuations. Resulting system of self-consistent equations is solved perturbatively in the long-wavelength limit. As a result, we have found two brunches of frequency dispersion: purely diffusive brunch corresponding to the lateral motion of U-forms, and damped bending modes of the membrane. Prediction is made for the spectral intensity distribution of the membrane’s fluctuations, that can be measured by e.g. neutron scattering technique. 2986-Pos Board B194 Analytical Calculation of Diffusion Coefficient Drop at the Liquid-Gel Phase Transition in Lipid Membrane Timur Galimzyanov1,2, Boris Kheyfets1, Sergei Mukhin1. 1 Theoretical Physics and Quantum Technologies, National University of Science and Technology MISIS, Moscow, Russian Federation, 2A.N. Frumkin Institute of Physical Chemistry and Electrochemistry RAS, Moscow, Russian Federation. Diffusion coefficient drop by an order of magnitude at the liquid-gel phase transition in the lipid membranes so far was missing theoretical description. Subdiffusion regime, which takes place on 1ps-10ns timescale, is captured by our microscopic model and shows a jump of the self-diffusion coefficient. We developed the analytical theory of the first order liquid-gel phase transition of a lipid bilayer using the microscopic model of semi-flexible strings. We have shown that the van der Waals attraction between the lipids tails is the essential component of the free energy. In the framework of the free volume theory, we calculated a diffusion coefficient in the subdiffusive regime drop by an order of magnitude at the main phase transition. We found that the main contribution to the diffusion drop is due to compression factor as opposed to activation-like factor. The calculated temperature dependencies of the major thermodynamic characteristics of the lipid membranes including diffusion coefficient, membrane thickness, area and volume per lipid molecule are in a good quantitative