Roles of carbonyl oxygens at the bilayer interface in phospholipid-sterol interaction.

Abstract

FROM many recent studies on the phospholipid–sterol interaction, it has become increasingly clear that the 3 α-and 3 β-hydroxy isomers of a range of sterols have quite different effects on the molecular mobility and functional property of lipid bilayer membranes1,2. For example, the addition of cholesterol or Δ5-cholesten-3 β-ol to liposomes decreases their permeability, whereas epicholesterol, a 3 α-isomer of cholesterol, exerts no apparent effect. It has been proposed that the 3 β-hydroxyl group engages in hydrogen bonding with the carbonyl oxygen of the fatty acyl groups in phospholipids in the bilayer3. Evidence supporting such hydrogen bond formation is strong4. The problem is, then, why does the 3 β-OH group of cholesterol, but not the 3 α-OH group of epicholesterol form such bonds?