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Chaisson EH, Heberle FA, Doktorova M. Building Asymmetric Lipid Bilayers for Molecular Dynamics Simulations: What Methods Exist and How to Choose One? MEMBRANES 2023; 13:629. [PMID: 37504995 PMCID: PMC10384462 DOI: 10.3390/membranes13070629] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2023] [Revised: 06/20/2023] [Accepted: 06/25/2023] [Indexed: 07/29/2023]
Abstract
The compositional asymmetry of biological membranes has attracted significant attention over the last decade. Harboring more differences from symmetric membranes than previously appreciated, asymmetric bilayers have proven quite challenging to study with familiar concepts and techniques, leaving many unanswered questions about the reach of the asymmetry effects. One particular area of active research is the computational investigation of composition- and number-asymmetric lipid bilayers with molecular dynamics (MD) simulations. Offering a high level of detail into the organization and properties of the simulated systems, MD has emerged as an indispensable tool in the study of membrane asymmetry. However, the realization that results depend heavily on the protocol used for constructing the asymmetric bilayer models has sparked an ongoing debate about how to choose the most appropriate approach. Here we discuss the underlying source of the discrepant results and review the existing methods for creating asymmetric bilayers for MD simulations. Considering the available data, we argue that each method is well suited for specific applications and hence there is no single best approach. Instead, the choice of a construction protocol-and consequently, its perceived accuracy-must be based primarily on the scientific question that the simulations are designed to address.
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Affiliation(s)
- Emily H. Chaisson
- Department of Chemistry, University of Tennessee Knoxville, Knoxville, TN 37916, USA
| | - Frederick A. Heberle
- Department of Chemistry, University of Tennessee Knoxville, Knoxville, TN 37916, USA
| | - Milka Doktorova
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA 22903, USA
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2
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Li X, Zhou S, Lin X. Molecular View on the Impact of DHA Molecules on the Physical Properties of a Model Cell Membrane. J Chem Inf Model 2022; 62:2421-2431. [PMID: 35513897 DOI: 10.1021/acs.jcim.2c00074] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Docosahexaenoic acid (DHA) is a ω-3 polyunsaturated fatty acid, which can be uptaken by cells and is essential for proper neuronal and retinal function. However, the detailed physical impact of DHA molecules on the plasma membrane is still unclear. Hence, in this work, we carried out μs-scale coarse-grained molecular dynamics (MD) simulations to reveal the interactions between DHA molecules and a model cell membrane. As is known, the cell membrane can segregate into liquid-ordered (Lo) and liquid-disordered (Ld) membrane domains due to the differential interactions between lipids and proteins. In order to capture this feature, we adopted the three-component phase-separated lipid membranes and considered both anionic and neutral DHA molecules in the current work. Our results showed that DHA molecules can spontaneously self-assemble into nanoclusters, fuse with lipid membranes, and localize preferably in Ld membrane domains. During the membrane fusion process, DHA molecules can change the intrinsic transmembrane potential of the lipid membrane, and the effects of anionic DHA molecules are much more significant. Besides, the presence of DHA molecules mainly in the Ld membrane domains could regulate the differences in the lipid chain order, membrane thickness, cholesterol preference, and cholesterol flip-flop basically in a concentration-dependent manner, which further promote the stability of the intraleaflet dynamics and inhibit the interleaflet dynamics (or promote membrane domain registration) of the membrane domains. In short, the impact of DHA molecules on the physical properties of a model cell membrane on the molecular level revealed in our work will provide useful insights for understanding the biological functions of DHA molecules.
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Affiliation(s)
- Xiu Li
- Beijing Advanced Innovation Center for Biomedical Engineering, School of Engineering Medicine & School of Biological Science and Medical Engineering, Beihang University, Beijing 100191, China
| | - Shiying Zhou
- Beijing Advanced Innovation Center for Biomedical Engineering, School of Engineering Medicine & School of Biological Science and Medical Engineering, Beihang University, Beijing 100191, China
| | - Xubo Lin
- Beijing Advanced Innovation Center for Biomedical Engineering, School of Engineering Medicine & School of Biological Science and Medical Engineering, Beihang University, Beijing 100191, China
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3
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Sharma A, Seal A, Iyer SS, Srivastava A. Enthalpic and entropic contributions to interleaflet coupling drive domain registration and antiregistration in biological membrane. Phys Rev E 2022; 105:044408. [PMID: 35590589 DOI: 10.1103/physreve.105.044408] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2021] [Accepted: 03/14/2022] [Indexed: 06/15/2023]
Abstract
Biological membrane is a complex self-assembly of lipids, sterols, and proteins organized as a fluid bilayer of two closely stacked lipid leaflets. Differential molecular interactions among its diverse constituents give rise to heterogeneities in the membrane lateral organization. Under certain conditions, heterogeneities in the two leaflets can be spatially synchronized and exist as registered domains across the bilayer. Several contrasting theories behind mechanisms that induce registration of nanoscale domains have been suggested. Following a recent study showing the effect of position of lipid tail unsaturation on domain registration behavior, we decided to develop an analytical theory to elucidate the driving forces that create and maintain domain registry across leaflets. Towards this, we formulated a Hamiltonian for a stacked lattice system where site variables capture the lipid molecular properties such as the position of unsaturation and various other interactions that could drive phase separation and interleaflet coupling. We solve the Hamiltonian using Monte Carlo simulations and create a complete phase diagram that reports the presence or absence of registered domains as a function of various Hamiltonian parameters. We find that the interleaflet coupling should be described as a competing enthalpic contribution due to interaction of lipid tail termini, primarily due to saturated-saturated interactions, and an interleaflet entropic contribution from overlap of unsaturated tail termini. A higher position of unsaturation is seen to provide weaker interleaflet coupling. Thermodynamically stable nanodomains could also be observed for certain points in the parameter space in our bilayer model, which were further verified by carrying out extended Monte Carlo simulations. These persistent noncoalescing registered nanodomains close to the lower end of the accepted nanodomain size range also point towards a possible "nanoscale" emulsion description of lateral heterogeneities in biological membrane leaflets.
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Affiliation(s)
- Akshara Sharma
- Department of Physics, Indian Institute of Science-Bangalore, C. V. Raman Road, Bangalore, Karnataka 560012, India
| | - Aniruddha Seal
- School of Chemical Sciences, National Institute of Science Education and Research, Bhubaneswar, Khurda, Odisha 752050, India
| | - Sahithya S Iyer
- Molecular Biophysics Unit, Indian Institute of Science-Bangalore, C. V. Raman Road, Bangalore, Karnataka 560012, India
| | - Anand Srivastava
- Molecular Biophysics Unit, Indian Institute of Science-Bangalore, C. V. Raman Road, Bangalore, Karnataka 560012, India
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4
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Keller F, Heuer A. Chain ordering of phospholipids in membranes containing cholesterol: what matters? SOFT MATTER 2021; 17:6098-6108. [PMID: 34100059 DOI: 10.1039/d1sm00459j] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Cholesterol (CHOL) drives lipid segregation and is thus a key player for the formation of lipid rafts and followingly for the ability of a cell to, e.g., enable selective agglomeration of proteins. The lipid segregation is driven by cholesterol's affinity for saturated lipids, which stands directly in relation to the ability of cholesterol to order the individual phospholipid (PL) acyl chains. In this work, molecular dynamics simulations of DPPC (dipalmitoylphosphatidylcholine, saturated lipid) and DLiPC (dilineoylphosphatidylcholine, unsaturated lipid) mixtures with cholesterol are used to elucidate the underlying mechanisms of the cholesterol ordering effect. To this end, all enthalpic contributions, experienced by the PL molecules, are recorded as a function of the PL's acyl chain order. This involves the PL-PL, the PL-cholesterol interaction, the interaction of the PLs with water, and the interleaflet interaction. This systematic analysis allows one to unravel differences of saturated and unsaturated lipids in terms of the different interaction factors. It turns out that cholesterol's impact on chain ordering stems not only from direct interactions with the PLs but is also indirectly present in the other energy contributions. Furthermore, the analysis sheds light on the relevance of the entropic contributions, related to the degrees of freedom of the acyl chain.
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Affiliation(s)
- Fabian Keller
- Institute of Physical Chemistry, University of Münster, Corrensstraße 28, 48149 Münster, Germany.
| | - Andreas Heuer
- Institute of Physical Chemistry, University of Münster, Corrensstraße 28, 48149 Münster, Germany.
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5
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Lipid asymmetry of a model mitochondrial outer membrane affects Bax-dependent permeabilization. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2020; 1862:183241. [DOI: 10.1016/j.bbamem.2020.183241] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/29/2019] [Revised: 01/16/2020] [Accepted: 02/12/2020] [Indexed: 11/24/2022]
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6
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Blumer M, Harris S, Li M, Martinez L, Untereiner M, Saeta PN, Carpenter TS, Ingólfsson HI, Bennett WFD. Simulations of Asymmetric Membranes Illustrate Cooperative Leaflet Coupling and Lipid Adaptability. Front Cell Dev Biol 2020; 8:575. [PMID: 32850783 PMCID: PMC7396604 DOI: 10.3389/fcell.2020.00575] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2020] [Accepted: 06/15/2020] [Indexed: 01/31/2023] Open
Abstract
Biological membranes are composed of lipid bilayers that are often asymmetric with regards to the lipid composition and/or aqueous solvent they separate. Studying lipid asymmetry both experimentally and computationally is challenging. Molecular dynamics simulations of lipid bilayers with asymmetry are difficult due to finite system sizes and time scales accessible to simulations. Due to the very slow flip-flop rate for phospholipids, one must first choose how many lipids are on each side of the bilayer, but the resulting bilayer may be unstable (or metastable) due to differing tensile and compressive forces between leaflets. Here we use molecular dynamics simulations to investigate a number of different asymmetric membrane systems, both with atomistic and coarse-grained models. Asymmetries studied include differences in number of lipids, lipid composition (unsaturated and saturated tails and different headgroups), and chemical gradients between the aqueous phases. Extensive analysis of the bilayers' properties such as area per lipid, density, and lateral pressure profiles are used to characterize bilayer asymmetry. We also address how cholesterol (which flip-flops relatively quickly) influences membrane asymmetries. Our results show how each leaflet is influenced by the other and can mitigate the structural changes to the bilayer overall structure. Cholesterol can respond to changes in bilayer asymmetry to alleviate some of the effect on the bilayer structure, but that will alter its leaflet distribution, which in turn affects its chemical potential. Ionic imbalances are shown to have a modest change in bilayer structure, despite large changes in the electrostatic potential. Bilayer asymmetry can also induce a modest electrostatic potential across the membrane. Our results highlight the importance of membrane asymmetry on bilayer properties, the influence of lipid headgroups, tails and cholesterol on asymmetry, and the ability of lipids to adapt to different environments.
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Affiliation(s)
- Madison Blumer
- Harvey Mudd College, Claremont, CA, United States.,Scripps College, Claremont, CA, United States
| | | | - Mengzhe Li
- Harvey Mudd College, Claremont, CA, United States.,Claremont McKenna College, Claremont, CA, United States
| | | | - Michael Untereiner
- Harvey Mudd College, Claremont, CA, United States.,Pomona College, Claremont, CA, United States
| | | | - Timothy S Carpenter
- Biochemical and Biophysical Systems Group, Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, Livermore, CA, United States
| | - Helgi I Ingólfsson
- Biochemical and Biophysical Systems Group, Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, Livermore, CA, United States
| | - W F Drew Bennett
- Biochemical and Biophysical Systems Group, Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, Livermore, CA, United States
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7
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Srivastava A, Debnath A. Asymmetry and Rippling in Mixed Surfactant Bilayers from All-Atom and Coarse-Grained Simulations: Interdigitation and Per Chain Entropy. J Phys Chem B 2020; 124:6420-6436. [DOI: 10.1021/acs.jpcb.0c03761] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- Arpita Srivastava
- Department of Chemistry, IIT Jodhpur, Jodhpur 342037, Rajasthan, India
| | - Ananya Debnath
- Department of Chemistry, IIT Jodhpur, Jodhpur 342037, Rajasthan, India
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8
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Mostofian B, Johnson QR, Smith JC, Cheng X. Carotenoids promote lateral packing and condensation of lipid membranes. Phys Chem Chem Phys 2020; 22:12281-12293. [PMID: 32432296 DOI: 10.1039/d0cp01031f] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Carotenoids are pigment molecules that protect biomembranes against degradation and may be involved in the formation of functional bacterial membrane microdomains. Little is known on whether different types of carotenoids have different effects on the membrane or if there is any concentration dependence of these effects. In this work, we present results from molecular dynamics simulations of phospholipid bilayers containing different amounts of either β-carotene or zeaxanthin. Both β-carotene and zeaxanthin show the ability to laterally condense the membrane lipids and reduce their inter-leaflet interactions. With increasing concentrations, both carotenoids increase the bilayer thickness and rigidity. The results reveal that carotenoids have similar effects to cholesterol on regulating the behavior of fluid-phase membranes, suggesting that they could function as sterol substitutes and confirming their potential role in the formation of functional membrane domains.
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Affiliation(s)
- Barmak Mostofian
- Center for Molecular Biophysics, Oak Ridge National Lab, Oak Ridge, TN 37830, USA.
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9
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Zhang S, Lin X. Lipid Acyl Chain cis Double Bond Position Modulates Membrane Domain Registration/Anti-Registration. J Am Chem Soc 2019; 141:15884-15890. [DOI: 10.1021/jacs.9b06977] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Siya Zhang
- Institute of Nanotechnology for Single Cell Analysis (INSCA), Beijing Advanced Innovation Center for Biomedical Engineering, Beihang University, Beijing 100191, China
- State Key Laboratory of Medical Molecular Biology, School of Basic Medicine, Peking Union Medical College and Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences, Beijing 100005, China
| | - Xubo Lin
- Institute of Nanotechnology for Single Cell Analysis (INSCA), Beijing Advanced Innovation Center for Biomedical Engineering, Beihang University, Beijing 100191, China
- School of Biological Science and Medical Engineering, Beihang University, Beijing 100191, China
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10
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Enkavi G, Javanainen M, Kulig W, Róg T, Vattulainen I. Multiscale Simulations of Biological Membranes: The Challenge To Understand Biological Phenomena in a Living Substance. Chem Rev 2019; 119:5607-5774. [PMID: 30859819 PMCID: PMC6727218 DOI: 10.1021/acs.chemrev.8b00538] [Citation(s) in RCA: 175] [Impact Index Per Article: 35.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2018] [Indexed: 12/23/2022]
Abstract
Biological membranes are tricky to investigate. They are complex in terms of molecular composition and structure, functional over a wide range of time scales, and characterized by nonequilibrium conditions. Because of all of these features, simulations are a great technique to study biomembrane behavior. A significant part of the functional processes in biological membranes takes place at the molecular level; thus computer simulations are the method of choice to explore how their properties emerge from specific molecular features and how the interplay among the numerous molecules gives rise to function over spatial and time scales larger than the molecular ones. In this review, we focus on this broad theme. We discuss the current state-of-the-art of biomembrane simulations that, until now, have largely focused on a rather narrow picture of the complexity of the membranes. Given this, we also discuss the challenges that we should unravel in the foreseeable future. Numerous features such as the actin-cytoskeleton network, the glycocalyx network, and nonequilibrium transport under ATP-driven conditions have so far received very little attention; however, the potential of simulations to solve them would be exceptionally high. A major milestone for this research would be that one day we could say that computer simulations genuinely research biological membranes, not just lipid bilayers.
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Affiliation(s)
- Giray Enkavi
- Department
of Physics, University of
Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
| | - Matti Javanainen
- Department
of Physics, University of
Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
- Institute
of Organic Chemistry and Biochemistry of the Czech Academy
of Sciences, Flemingovo naḿesti 542/2, 16610 Prague, Czech Republic
- Computational
Physics Laboratory, Tampere University, P.O. Box 692, FI-33014 Tampere, Finland
| | - Waldemar Kulig
- Department
of Physics, University of
Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
| | - Tomasz Róg
- Department
of Physics, University of
Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
- Computational
Physics Laboratory, Tampere University, P.O. Box 692, FI-33014 Tampere, Finland
| | - Ilpo Vattulainen
- Department
of Physics, University of
Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
- Computational
Physics Laboratory, Tampere University, P.O. Box 692, FI-33014 Tampere, Finland
- MEMPHYS-Center
for Biomembrane Physics
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11
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Weiner MD, Feigenson GW. Molecular Dynamics Simulations Reveal Leaflet Coupling in Compositionally Asymmetric Phase-Separated Lipid Membranes. J Phys Chem B 2019; 123:3968-3975. [PMID: 31009218 DOI: 10.1021/acs.jpcb.9b03488] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The eukaryotic plasma membrane has an asymmetric distribution of its component lipids. Rafts that result from liquid-liquid phase separation are a feature of its exoplasmic leaflet, but how these exoplasmic leaflet domains are coupled to the cytoplasmic leaflet is not understood. These rafts can be studied in model membranes of three-component mixtures that produce coexisting liquid ordered (Lo) and liquid disordered (Ld) domains. We conducted all-atom molecular dynamics simulations of compositionally asymmetric lipid bilayers that reflect a more realistic model of the plasma membrane. One leaflet contained phase-separated domains with phosphatidylcholine and cholesterol, representing the exoplasmic leaflet, whereas the other contained phosphatidylethanolamine, phosphatidylserine, and cholesterol, which are the predominant components of the cytoplasmic leaflet. Inspired by findings of domain alignment across the two leaflets in compositionally symmetric model membranes, we examined the coupling between the two leaflets to see how the single-phase cytoplasmic leaflet would respond to phase separation in the other leaflet and if information could be communicated across the membrane. We found the region of the single-phase leaflet apposing the Lo domain to be slightly more ordered and thicker than the region apposing the Ld domain. The region across from the Lo domain is somewhat enriched in cholesterol and significantly depleted of polyunsaturated lipids.
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12
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Affiliation(s)
- Xiaolin Cheng
- Division of Medicinal Chemistry and Pharmacognosy, Biophysics Graduate Program, Translational Data Analytics Institute, The Ohio State University, Columbus, Ohio 43210, United States
| | - Jeremy C. Smith
- UT/ORNL Center for Molecular Biophysics, Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6309, United States
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee 37996, United States
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13
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Accurate In Silico Modeling of Asymmetric Bilayers Based on Biophysical Principles. Biophys J 2018; 115:1638-1643. [PMID: 30297133 DOI: 10.1016/j.bpj.2018.09.008] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2018] [Revised: 08/20/2018] [Accepted: 09/07/2018] [Indexed: 12/24/2022] Open
Abstract
Technological advances in the last decade have enabled the study of ever more complex and physiologically relevant model membranes to help dispel the mystery surrounding the role of plasma membrane asymmetry in various cellular processes. The slowly accumulating body of experimental data is fueling renewed interest in and the need for computational methods to support interpretations and address a wide range of problems that are still not amenable to direct experimental study. The specific appeal of molecular dynamics simulations for this purpose lies in their ability to access information at atomic resolution, which is useful for the formulation of testable mechanistic hypotheses. But, the range of questions that can be addressed reliably with such simulations is determined by the appropriate construction and simulation of asymmetric bilayer models. One essential way to achieve this goal is to follow rigorous biophysical criteria and principles. In this context, we show that the requirement for a robust comparison between the properties of simulated asymmetric and symmetric model membranes is for the tension in each bilayer leaflet to be zero. Commonly used methods for constructing asymmetric bilayers, including matching the average areas of the leaflets from the corresponding symmetric systems, do not ensure zero leaflet tension, thus precluding physically realistic changes in the areas of the two leaflets. We present, to our knowledge, a new method for identifying the ideal lipid packing in bilayers with different leaflet compositions that achieves the zero-tension goal, and discuss the basic principles underlying the biophysically correct computational study of asymmetric membranes.
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14
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Lin X, Zhang S, Ding H, Levental I, Gorfe AA. The aliphatic chain of cholesterol modulates bilayer interleaflet coupling and domain registration. FEBS Lett 2016; 590:3368-3374. [PMID: 27590031 DOI: 10.1002/1873-3468.12383] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2016] [Revised: 08/25/2016] [Accepted: 08/29/2016] [Indexed: 11/10/2022]
Abstract
Cholesterol is a necessary component and critical regulator of liquid-ordered membrane domains. However, the structural features that determine its unique physicochemical behaviors are not fully understood. In particular, very little is known about the specific functions of the terminal aliphatic chain of cholesterol, as previous studies have focused mainly on the rigid sterol ring structure and its hydroxyl head. In the current work, we used coarse-grained molecular dynamics simulations to investigate the effect of cholesterol aliphatic chain length on the dynamics and structure of coexisting lipid domains. We found that the aliphatic chain has no appreciable effect on phase separation per se, but it significantly affects the rate of cholesterol flip-flop and intermonolayer interaction. These effects are accompanied by changes in domain dynamics, lateral pressure, and interleaflet coupling. Our study provides useful insight into how biological sterols modulate communication between the outer and inner surfaces of the plasma membrane and, therefore, cellular signaling.
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Affiliation(s)
- Xubo Lin
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Texas 77030, USA
| | - Siya Zhang
- State Key Laboratory of Medical Molecular Biology, School of Basic Medicine, Peking Union Medical College and Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences, Beijing 100005, China.,Department of Immunology, The University of Texas MD Anderson Cancer Center, Texas 77054, USA
| | - Hui Ding
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Texas 77030, USA.,Department of Respiratory Medicine, Yixing Hospital affiliated Jiangsu University, Jiangsu 214200, China
| | - Ilya Levental
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Texas 77030, USA
| | - Alemayehu A Gorfe
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Texas 77030, USA
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