Flicker Spectroscopy of Thermal Lipid Bilayer Domain Boundary Fluctuations

Abstract

This contribution describes measurements of lipid bilayer domain line tension based on two-dimensional thermal undulations of membranes with liquid ordered/liquid disordered phase coexistence and near-critical composition at room temperature. Lateral inhomogeneity of lipid and protein composition is currently a subject of avid research aimed at determining both fundamental properties and biological relevance of membrane domains. Line tension at fluid lipid bilayer membrane domain boundaries controls the kinetics of domain growth and therefore regulates the size of compositional heterogeneities. High line tension promotes membrane domain budding and fission. Line tension could therefore be an important control parameter regulating functional aspects of biological membranes. Here the established method of fluid domain flicker spectroscopy is applied to examine thermal domain wall fluctuations of phase-separated bilayer membranes. We find a Gaussian probability distribution for the first few excited mode amplitudes, which permits an analysis by means of appropriately specialized capillary wave theory. Time autocorrelation functions are found to decay exponentially, and relaxation times are fitted by means of a hydrodynamic theory relating line tensions and excited mode relaxation kinetics. Line tensions below 1 pN are obtained, with these two approaches yielding similar results. We examine experimental artifacts that perturb the Fourier spectrum of domain traces and discuss ways to identify the number of modes that yield reliable line tension information.

Membrane heterogeneity – from lipid domains to curvature effects

“…2 of this thesis) including line tension and the difference in Gaussian bending moduli between the two phases. Alternatively, domain boundary fluctuations can be used to retrieve the line tension (22,84). Consistently, line tension around 1pN are found far away from the critical point where domain boundary fluctuations are absent.…”

Bile Acids Modulate Signaling by Functional Perturbation of Plasma Membrane Domains

“…These bulky lipids, such as branched and polyunsaturated lipids, form coexisting, relatively disordered domains (19). This immiscibility gives rise to coexistence of two liquid membrane phases in model bilayers (16,18) and isolated bio-logical membranes (20,21), and these have been used as a model for cholesterol-dependent domains in live cells (for review, see Refs. 19,[22][23][24][25][26].…”

“…Phase separation into coexisting lipid-driven domains of varying compositions and physical properties can be observed in plasma membranes isolated from live cells, termed giant plasma membrane vesicles (GPMVs) 3 (21,27). Conceptually, the observation of two coexistent, lipid-driven, liquid phases in a membrane that maintains the lipid and protein diversity of the native plasma membrane provides a critical validation of the raft hypothesis.…”

Hallmarks of Reversible Phase Separation in Living, Unperturbed Cell Membranes

“…[37][38][39][40][41][42][43][44] Below the critical temperature, domains boundaries fluctuate through time such that domains appear to wiggle. 39,45,46 The characteristic length scale of these fluctuations varies with temperature. Near the critical point, the fraction of the GUV's surface area covered…”