Model Membrane Systems Used to Study Plasma Membrane Lipid Asymmetry.

John Katsaras,Thais A. Enoki,Jacob J. Kinnun,Milka Doktorova,Kristen B. Kennison,Frederick A. Heberle,Haden L. Scott

doi:10.3390/sym13081356

Abstract

It is well known that the lipid distribution in the bilayer leaflets of mammalian plasma membranes (PMs) is not symmetric. Despite this, model membrane studies have largely relied on chemically symmetric model membranes for the study of lipid–lipid and lipid–protein interactions. This is primarily due to the difficulty in preparing stable, asymmetric model membranes that are amenable to biophysical studies. However, in the last 20 years, efforts have been made in producing more biologically faithful model membranes. Here, we review several recently developed experimental and computational techniques for the robust generation of asymmetric model membranes and highlight a new and particularly promising technique to study membrane asymmetry.

Highlights

The mammalian plasma membrane (PM) is composed of lipids and proteins, both peripheral and integral, that are chemically diverse and non-randomly distributed
This largely changed with the development of CD-mediated lipid exchange that has allowed for the reproducible preparation of stable asymmetric vesicles and has led to the development of other methods of preparing asymmetric membranes
The techniques described in this review are sufficiently developed to be used in studies that will expand our understanding of PM asymmetry, and begin to tease out the many mysteries associated with this important membrane feature

Summary

Introduction

The mammalian plasma membrane (PM) is composed of lipids and proteins, both peripheral and integral, that are chemically diverse and non-randomly distributed. Most phospholipids in the cytoplasmic leaflet possess one or more unsaturations in their sn-2 chains [7] On average, this lipid asymmetry results in a PM with a more ordered extracellular leaflet, compared to its cytoplasmic counterpart [7,8]. Transient loss of PM lipid asymmetry has been reported in different cellular contexts, including intercellular communication, cell-cell contact, and intracellular signaling, further demonstrating membrane asymmetry’s vital role in a wide array of biological processes [24]. Recent advances have made the generation of asymmetric model membranes much more practical, enabling one to study the intricacies of lipid–lipid and protein-lipid interactions under more biologically relevant conditions. We focus on molecular dynamics (MD) simulations of asymmetric membranes

Techniques Used to Prepare Asymmetric Membranes In Vitro

Asymmetric Large Unilamellar Vesicles

Enzymes as Tools to Generate Asymmetric Vesicles

Using Cyclodextrins to Generate Asymmetric Vesicles

Giant Unilamellar Vesicles and Membrane Asymmetry

Preparation of aGUVs by MβCD-Mediated Lipid Exchange

Cholesterol-Rich aGUVs Made Using MβCD-Mediated Lipid Exchange

Hemifusion and aGUVs

Findings

Concluding Remarks