Lattice simulations of phase morphology on lipid bilayers: Renormalization, membrane shape, and electrostatic dipole interactions

Abstract

When liquid phases coexist at equilibrium but are not driven to minimize domain interfacial contact energy, the resulting patterns of phase domains can have important implications for living cells. In this study we explore some of the interactions and conditions that produce the stable patterned phases that are observed in model lipid mixtures. By use of Monte Carlo simulations we find that background curvature is important for the formation of patterned (modulated) phases. The interactions that stabilize nanoscopic phase separation are still not well understood. We show that inclusion of an electrostatic dipole repulsion with decay lengths as short as two to four lipid diameters can break up domains at the nanometer scale and that the location of the miscibility critical point is sensitive to this interaction. The use of a coarse-grained simulation raises questions about comparing parameters in simulations performed at different length scales. Using renormalization group techniques we show how to reconcile this problem, treating line tension as a running coupling constant.

Modulation of lipid membrane structural and mechanical properties by a peptidomimetic derived from reduced amide scaffold

“…Within a certain distance range r , the pair distribution function G(r) decays exponentially [64, 65]. The corresponding decay length is defined as the correlation length ξ.…”

Cholesterol-induced suppression of membrane elastic fluctuations at the atomistic level

“…Various membrane lipids exhibit lyotropic liquid-crystalline phases under physiological conditions, involving solid-ordered ( s o ), liquid-disordered ( l d ), and liquid-ordered ( l o ) phases. Attractive and repulsive forces for the membrane lipids entails both the polar headgroups and the non-polar moieties, and yield a substantial polymorphism with both lamellar and nonlamellar phases (Amazon and Feigenson, 2014; Brown, 1994; Feigenson, 2006, 2015; Gruner, 1989; Krepkiy et al, 2009; Phillips et al, 2009; Seddon, 1990; Seddon et al, 1997; van Meer et al, 2008; Zimmerberg and Gawrisch, 2006). Notably, the structural and dynamical properties of biomembranes are mediated by the lipid composition and interactions with the proteins, water, cholesterol, and surfactants (Brown and Chan, 2007; Coskun and Simons, 2011; Kaiser et al, 2009; Kaye et al, 2011; Kinnun et al, 2015; Leftin et al, 2014b; Mallikarjunaiah et al, 2011; Rheinstädter et al, 2004; Tyler et al, 2015).…”

“…On the other hand, it is known that many of the molecular species of lipids and proteins in membranes do not mix ideally (Ackerman and Feigenson, 2015; Amazon and Feigenson, 2014; Armstrong et al, 2012; Armstrong et al, 2013; Eriksson and Henriksson, 2007; Eriksson et al, 2006; Escriba et al, 2008; Feigenson, 2015; Goñi et al, 2008; Konyakhina and Feigenson, 2016). Cholesterol is one such component that may not be uniformly distributed in cellular membranes, whose distribution entails liquid-ordered raft-like domains (Ackerman and Feigenson, 2015; Amazon and Feigenson, 2014; Epand, 1998; Epand, 2006; Feigenson, 2015; Goñi et al, 2008; Konyakhina and Feigenson, 2016; Scheidt et al, 2013; Sodt et al, 2014).…”

“…Cholesterol is one such component that may not be uniformly distributed in cellular membranes, whose distribution entails liquid-ordered raft-like domains (Ackerman and Feigenson, 2015; Amazon and Feigenson, 2014; Epand, 1998; Epand, 2006; Feigenson, 2015; Goñi et al, 2008; Konyakhina and Feigenson, 2016; Scheidt et al, 2013; Sodt et al, 2014). Such raft-like domains have garnered considerable attention as platforms for signaling proteins in cellular biology and pharmacology (Brown and London, 1998; Day and Kenworthy, 2015; Golebiewska and Scarlata, 2010; Klose et al, 2013; Simons and Gerl, 2010; Simons and Sampaio, 2011; Song et al, 2014; Surma et al, 2012).…”

Composition fluctuations in lipid bilayers

“…Composition fluctuations can be distinguished from domains of coexisting phases by analyzing the inplane (2D) radial distribution function (RDF) (Figure 4a,b). For one-phase bilayers, the RDFs decay exponentially as the correlations in density are short-range; for phase-separated bilayers, the RDFs decay is linear due to long-range density correlations in the domains (34,40). Linear decay is followed by periodic undulations which correspond to the variation of densities of the lipid components between the two coexisting phases.…”