The effect of cholesterol, lanosterol and ergosterol on lecithin bilayer mechanical properties at molecular and microscopic dimensions : a solid-state NMR and micropipet study

Lecithin (DPPC) membranes doped with high concentrations (40 mol%) of three biologically relevant sterols (cholesterol, lanosterol, and ergosterol) were studied by spectroscopic and force measurements. Micropipet aspiration measurements of giant unilamellar vesicles provided the membrane area expansion modulus K on the microscopic scale while deuterium NMR experiments gave parameters such as the line shape, transverse relaxation, and molecular order, which are all based on a molecular scale at a given time resolution, Micropipet experiments at 10 degreesC gave K values for the three samples with ergosterol > cholesterol > lanosterol. From the NMR we obtained the highest CH2-segmental molecular order and longest transverse relaxation time for cholesterol and the opposite for ergosterol. The lanosterol NMR parameters were found to be between those of the other two sterols but were closer to those of cholesterol. The extent of deformation of the sterol-doped vesicles in the magnetic field of the NMR magnet was lanosterol > cholesterol > ergosterol. The results suggest that membrane micromechanic properties are manifest in solid-state NMR parameters and suggest that high K values at the microscopic scale correspond to high molecular order and long transverse relaxation times at the molecular scale. Furthermore, the extent of magnetic field orientation of vesicles measured by NMR correlated well with K determined by micropipet aspiration. The results may help to appreciate why cholesterol has gained a dominant role over the other sterols in the course of cellular evolution