In Vitro Studies on the Folding and Function of Lactose Permease in a Synthetic Lipid System

Abstract

Biological membranes are complex environments, where membrane proteins are surrounded by a bilayer composed of many different types of lipid. The physical properties of the bilayer influence protein structure, folding and function, while specific interactions with lipid molecules can also contribute towards the biological activity of some membrane proteins. Improving understanding of the interactions has resulted in the development of artifical lipid systems that allow the bilayer properties to be rationally manipulated in vitro to control protein behaviour. The bacterial transporter LacY is a well known integral membrane protein, responsible for the proton-driven uptake of D-lactose in E. coli. With a high resolution structure available and considerable understanding of mechanistic detail, and with observed changes to both structure and function in different bilayer environments, LacY is a good model system for examining the behaviour of a major class of membrane proteins in these lipid systems. Purified LacY has been folded and reconstituted into liposomes of varying synthetic lipid composition and the effect on protein topology and transport activity examined.