Interleaflet Decoupling in a Lipid Bilayer at Excess Cholesterol Probed by Spectroscopic Ellipsometry and Simulations
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Interleaflet Decoupling in a Lipid Bilayer at Excess Cholesterol Probed by Spectroscopic Ellipsometry and Simulations Sagar Kamble1 · Snehal Patil1 · Mandar Kulkarni2 · Venkata Ramana Murthy Appala1 Received: 7 July 2020 / Accepted: 11 November 2020 / Published online: 22 November 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Artificial lipid membranes are often investigated as a replica of the cell membrane in the form of supported lipid bilayers (SLBs). In SLBs, the phase state of a lipid bilayer strongly depends on the presence of molecules such as cholesterol, ceramide, and physical parameters such as temperature. Cholesterol is a key molecule of biological membranes and it exerts condensing effect on lipid bilayers. In this paper, we demonstrate the influence of excess cholesterol content on a supported lipid bilayer of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) (fluid-phase) using spectroscopic ellipsometry (SE) and coarse-grained (CG) molecular dynamics (MD) simulations. The results show the condensation effect due to cholesterol addition up to 30% and interleaflet decoupling at excess cholesterol beyond 30%. SE results show the separation of individual leaflets of the bilayer and influence of cholesterol on the biophysical properties such as thickness and optical index. CG simulations were performed at different ratios of DOPC:cholesterol mixtures to explore cholesterol-driven bilayer properties and stability. The simulations displayed the accumulation of cholesterol molecules at the interface of the lower and upper leaflets of the bilayer, thus leading to undulations in the bilayer. This work reports the successful application of SE technique to study lipid–cholesterol interactions for the first time. Graphical abstract
Keywords Lipid membranes · DOPC · Cholesterol · Spectroscopic ellipsometry · MARTINI force field · Coarse-grained simulations Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00232-020-00156-9) contains supplementary material, which is available to authorized users. * Mandar Kulkarni [email protected] * Venkata Ramana Murthy Appala [email protected] 1
Department of Applied Physics, Defence Institute of Advanced Technology (DIAT) DU, Girinagar, Pune, India
Division of Biophysical Chemistry, Chemical Center, Lund University, 22100 Lund, Sweden
2
Introduction Supported lipid bilayers (SLBs) are planar arrangements spontaneously formed due to the self-assembly of various lipids. SLBs can closely mimic the actual biological membranes at near-physiological conditions and hence are called biomimetic or artificial lipid membranes (Richter et al. 2006). Inspecting the biophysical aspects of these lipid membranes is straightforward compared to complex native biological membranes. The lateral organization of lipid
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membranes affects their biophysical properties and topography at the nanoscale (Eeman and Deleu 2010; Murthy et al. 2015). This is a well-establis
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