Lipid‐protein interactions as a determinant of the function and topogenesis of membrane proteins

Abstract

LacY (lactose permease) expressed in Escherichia coli lacking PE (phosphatidylethanolamine) and containing only anionic phospholipids exhibits downhill but not uphill transport and is topologically misassembled. Substitution in vivo of PE by foreign lipids (including phosphatidylcholine (PC)) with no net charge supports native LacY topology and uphill transport. Here, we further investigate the effects of phospholipid head group and fatty acid composition on topology and function of LacY reconstituted into proteoliposomes. Anionic phospholipids alone do not support uphill transport or native topology. Addition of E. coli derived PE or PC supports both uphill transport and native topology. Synthetic PE or PC containing only unsaturated fatty acids supports proper topology but not uphill transport. PE or PC with one saturated fatty acid supports uphill transport. These results show that LacY structure and function are sensitive to both the polar head group and acyl group composition of phospholipids. Our results demonstrate that membrane protein organization and function are determined through direct interactions of the protein with its lipid environment. Supported by NIH grant R37‐GM20478.