Properties of hopanoids and phosphatidylcholines containing ω-cyclohexane fatty acid in monolayer and liposome experiments

Abstract

1,2,3,4-Tetrahydroxypentane-29-hopane (THBH) and a glycolipid derived from it are associated with ω-cyclohexane fatty acids-containing lipids in the membrane of Bacillus acidocaldarius. In order to elucidate the function of these lipids we studied mixed monolayer films and compared these with cholesterol-containing films. The hopanoids are able to condense a liquid-expanded film of di-ω-cyclohexyldodecanoylphosphatidylcholine (DCDPC). The condensing effect of THBH is smaller than that of cholesterol. Hopane glycolipid in comparison shows only little condensation. In a more condensed film, at lower temperatures, THBH slightly decreases while hopane glycolipid increases the molecular area. In egg phosphatidylcholine liposomes, 22-hydroxyhopane (diplopterol) and hopane glycolipid reduce the glycerol permeability to a smaller extent than cholesterol. In DCDPC liposomes, the effect of 22-hydroxyhopane is similar to that of cholesterol, while the hopane glycolipid shows only a weak reduction of the permeability. The results demonstrate that hepanoids have a cholesterol-like function in membranes. This function is also discussed in the context of membrane adaptation of a thermoacidophilic bacterium.