Brownian Motion at Lipid Membranes: A Comparison of Hydrodynamic Models Describing and Experiments Quantifying Diffusion within Lipid Bilayers.

Stephan Block

doi:10.3390/biom8020030

Abstract

The capability of lipid bilayers to exhibit fluid-phase behavior is a fascinating property, which enables, for example, membrane-associated components, such as lipids (domains) and transmembrane proteins, to diffuse within the membrane. These diffusion processes are of paramount importance for cells, as they are for example involved in cell signaling processes or the recycling of membrane components, but also for recently developed analytical approaches, which use differences in the mobility for certain analytical purposes, such as in-membrane purification of membrane proteins or the analysis of multivalent interactions. Here, models describing the Brownian motion of membrane inclusions (lipids, peptides, proteins, and complexes thereof) in model bilayers (giant unilamellar vesicles, black lipid membranes, supported lipid bilayers) are summarized and model predictions are compared with the available experimental data, thereby allowing for evaluating the validity of the introduced models. It will be shown that models describing the diffusion in freestanding (Saffman-Delbrück and Hughes-Pailthorpe-White model) and supported bilayers (the Evans-Sackmann model) are well supported by experiments, though only few experimental studies have been published so far for the latter case, calling for additional tests to reach the same level of experimental confirmation that is currently available for the case of freestanding bilayers.

Highlights

Bilayers that are formed by self-assembly of lipid molecules represent one of the major building blocks found in nature [1]
(c) Differences in the mobility or size of virus membrane-associated objects can be used for analytical purposes in the diffusion is, for example, expected to be one way to increase the overall virus–membrane interaction presence of a hydrodynamic shear force. This concept has been by subsequently increasing the number of receptors engaged by the virus, a process that is promoted by diffusion of the virus and/or the membrane-bound receptors (HA: hemagglutinin; PDB code 1RD8). (c) Differences in the mobility or size of membrane-associated objects can be used for analytical purposes in the presence of a hydrodynamic shear force
This review aims to summarize the different theories developed to describe diffusion within lipid bilayers and to provide a comparison between the theoretical predictions and recent experimental demonstrations using the aforementioned model systems

Summary

Introduction

Bilayers that are formed by self-assembly of lipid molecules represent one of the major building blocks found in nature [1]. (c) Differences in the mobility or size of virus membrane-associated objects (e.g., proteins, liposomes) can be used for analytical purposes in the diffusion is, for example, expected to be one way to increase the overall virus–membrane interaction presence of a hydrodynamic shear force (e.g., created by a microfluidic environment) This concept has been by subsequently increasing the number of receptors engaged by the virus (see insets), a process that is promoted by diffusion of the virus and/or the membrane-bound receptors (HA: hemagglutinin; PDB code 1RD8). It will be shown that models describing diffusion of such inclusions in freestanding bilayers (i.e., the Saffman-Delbrück and the Hughes-Pailthorpe-White model) have been mostly confirmed experimentally with respect to variations in the inclusion radius, while the case of bilayers being supported by solid substrates has been less well addressed experimentally

Models of Membrane Hydrodynamics

Overview

Abbreviations: black lipid

Dependence of of reduced from reduced

Conclusions