The Effect of Cholesterol, Lanosterol, and Ergosterol on Lecithin Bilayer Mechanical Properties at Molecular and Microscopic Dimensions:  A Solid-State NMR and Micropipet Study

Abstract

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°C 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.

Line tension of the pore edge in phospholipid/cholesterol bilayer from stretch molecular dynamics simulation

“…(5), the area compressibility modulus KA can be calculated as 306, 402, and 760 mN/m, respectively. KA increases with the increase of the cholesterol concentration, which is in qualitative agreement with that observed from experiments (Endress et al, 2002;Needham and Nunn, 1990). Using these parameters A0, KA, and c in Fig.…”

Investigating the impact of cholesterol on magnetically aligned sphingomyelin/cholesterol multilamellar vesicles using static 31P NMR

“…This result is consistent with the reduction in orientation observed for egg phosphatidylcholine (PC)/Chol (Qiu et al, 1993) but conflicts with the increased magnetic alignment observed for a DPPC/Chol system (Brumm et al, 1992;Reinl and Bayerl, 1992;Endress et al, 2002) Measurements of the elastic area compressibility modulus, K m (proportional to Ä, Eq. (1)) by micromechanical techniques of SM and saturated PC GLVs with 50 mol% Chol (McIntosh et al, 1992) reveal K m values more than 2.3 larger (perhaps reflecting increased cholesterol association) than those reported for DPPC/40 mol% Chol (Endress et al, 2002). It is possible the increased membrane curvature energy for SM/Chol and PC/Chol bilayers suppresses the degree of magnetic deformation in these systems.…”

“…In addition, conflicting results have been reported for mixed phospholipid/cholesterol systems. For DPPC/30% Chol, the degree of magnetic alignment increases as cholesterol is added (Brumm et al, 1992;Reinl and Bayerl, 1992;Endress et al, 2002). However, for an egg PC liposome, a decrease in the percent of aligned phospholipids was observed when 30% cholesterol was added above T m (Qiu et al, 1993).…”

Cholesterol-induced suppression of membrane elastic fluctuations at the atomistic level

“…In terms of biomolecular NMR spectroscopy, it has been observed that the slope of square-law plot is greater for lanosterol than for cholesterol, consistent with the bilayer stiffness being less for lanosterol versus its metabolic product cholesterol (Martinez et al, 2004; Orädd et al, 2009; Shahedi et al, 2006). Again, it is found that the site-specific analysis of the solid-state NMR results based on atomistic observables matches the results for the macroscopic bilayer elasticity (Endress et al, 2002a; Endress et al, 2002b) (Fig. 9).…”