Effect of surface curvature on the rate of cholesterol transfer between lipid vesicles

Abstract

The effect of surface curvature on the spontaneous movement of cholesterol between membranes was investigated by measuring the rates of cholesterol transfer from donor vesicles of various sizes to a common acceptor vesicle. Donor vesicles of size in the range 40-240 nm were prepared by extruding multilamellar dispersions through polycarbonate filters of different pore sizes under pressure. The smallest donor vesicle and the acceptor vesicles were obtained by the normal sonication procedures. The rate of cholesterol transfer, as measured by the movement of [3H]cholesterol, decreases with increasing size of the donor vesicle in an almost linear fashion. The extrapolation of the results gave a half-time (t1/2) of 16-20 h of the desorption of cholesterol from a planar bilayer, and this can be considered as a reference value for most cellular membranes which are characterized by very low curvatures. Our earlier studies have shown that the t1/2 for cholesterol efflux is influenced by the presence of gangliosides and phosphatidylethanolamine, and the asymmetric distribution of these lipids in the plasma membrane could partially account for the large difference in the rates of cholesterol movement from the two sides of the plasma membrane. The small differences in rates arising from asymmetric distribution will be magnified by the longer t1/2 obtained here for membranes of low curvatures, so that the large difference in rates might be a coupled effect of lipid asymmetry and low curvature of the plasma membrane. This, in turn, may have a role in maintaining the large differences in cholesterol/phospholipid molar ratios observed between plasma membrane and intracellular membranes.

Is Spontaneous Translocation of Polar Lipids between Cellular Organelles Negligible?

“…For instance, McLean and Phillips found that the half-time for cholesterol translocation between vesicles is only 2.4 hours, 23 which is an order of magnitude less than the corresponding value for intact GPLs (see above). A similar value has been found by others, 24,25 and even faster rates (~1 hour) have been reported. 14 The rate of the spontaneous transfer of ergosterol (the cholesterol equivalent in yeast) has not been determined, but it is probably even faster than that of cholesterol due to the presence of two additional double bonds, albeit there is an extra methyl group in ergosterol.…”

Stabilization of α-Synuclein Secondary Structure upon Binding to Synthetic Membranes

“…The phospholipid bilayer of an LUV is an essentially planar surface in which the fatty acyl side chains are motionally restricted (32), compared with the curved surface of an SUV (33). It has been demonstrated that the initial insertion of the amphipathic ␣-helical regions of plasma lipoproteins into a phospholipid bilayer is facilitated by the existence of lipid packing defects caused by extreme membrane curvature or by the differential packing properties of different phospholipids within the membrane (34).…”

Spontaneous lipid transfer between organized lipid assemblies

“…For many years, it has been known that spontaneous cholesterol exchange is faster from small sonicated bilayer vesicles than from larger, planar-like bilayers vesicles [70,[121][122]. Indeed, for the case of cholesterol and zwitterionic diacyl phopholipids [70,[121][122], it appears that the characteristics of the donor rather than the acceptor vesicles limit the transfer rate. In fact, the association rate of PC monomers with neutral acceptor vesicles has generally been thought to be diffusion limited by the aqueous mileu rather than by the interfacial characteristics of the acceptor surface [123].…”