The Effect of Hydrophobic Matching between Lipids and Transmembrane Peptides on Sterol Bilayer Affinity

Abstract

Lipid self-organization is believed to be essential for shaping the lateral structure of membranes, but it is becoming increasingly clear that also membrane proteins can be involved in the maintenance of membrane architecture. Cholesterol is thought to be important for the lateral organization of eukaryotic cell membranes and has also been implicated to take part in the sorting of cellular transmembrane proteins. It is therefore of interest to study the influence of lipid-protein interactions on membrane trafficking to find out how transmembrane proteins influence the lateral sorting of cholesterol in phospholipid bilayers. We have measured the equilibrium partitioning of the fluorescent cholesterol analog cholestatrienol between large unilamellar vesicles and methyl-β-cyclodextrin to determine the effect of hydrophobic matching on the affinity of sterols for phospholipid bilayers. The sterol partitioning was measured in 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayers with and without the peptides WALP19, WALP23 or WALP27. The results showed that hydrophobic matching will affect the affinity of the sterol for the bilayers. Stronger sterol binding to the bilayers was achieved by an increase in positive hydrophobic mismatch (except in extreme situations), and a large negative hydrophobic mismatch decreased the affinity of the sterol for the bilayer. Peptide insertion into the phospholipid bilayers was also observed to depend on hydrophobic matching. In conclusion, the results showed that hydrophobic matching can affect lipid-protein interactions in a way that may facilitate the formation of lateral domains in cell membranes. This may well be of importance in membrane trafficking.