Lanosterol and cholesterol-induced variations in bilayer elasticity probed by 2H NMR relaxation.

The influences of lanosterol on lipid bilayers have been compared to those of cholesterol by combining deuterium (2H) NMR spin relaxation studies with segmental order parameter measurements. For bilayers of 1,2-diperdeuteriomyristoyl-sn-glycero-3-phosphocholine (DMPC-d54), the results are consistent with a square-law dependence of the 2H Zeeman relaxation rates (R1Z) on the corresponding order parameters (SCD). This behavior is indicative of relatively slow order fluctuations, for example, due to quasi-elastic bilayer disturbances. Significant differences are found in the influences of lanosterol versus cholesterol on the microscopic NMR observables; although lanosterol produces smaller order parameters than cholesterol, it leads to larger relaxation rates. By correlating the NMR relaxation behavior with the order parameters, the results are explained by a progressive reduction of the bilayer elasticity, which parallels the biosynthetic pathway from lanosterol to cholesterol.