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-d ₅₄), the results are consistent with a square-law dependence of the ²H Zeeman relaxation rates (R _1Z) on the corresponding order parameters (S _CD). 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.