Intrinsic proteins and their effect upon lipid hydrocarbon chain order

Abstract

At temperatures greater than their main transition temperature, phospholipid molecules that are trapped within clusters of intrinsic molecules such as polypeptides or proteins have the ends of their hydrocarbon chains more statically disordered than those of lipid molecules far from such intrinsic molecules. A model was constructed in which the lipids are divided into 3 populations: those that are not adjacent to any protein (free lipids), those that are adjacent to only 1 protein (adjacent lipids), and those that trapped between 2 or 3 proteins. This model was applied to study deuterium NMR of dimyristoyl-3-sn-phosphatidylcholine (DMPC) bilayers containing gramicidin A'' or cytochrome oxidase and while the methyl groups of adjacent lipids are slightly more statically ordered than those of free lipids, the methyl groups of trapped lipids are more statically disordered than those of free lipids. A physical explanation is proposed for this and it is shown that P-31 NMR data for DMPC-cytochrome oxidase bilayers can be understood as a consequence of changes in the polar region of only trapped lipids.