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 membranes^1,2. 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?