Lateral diffusion of erythrocyte phospholipids in model membranes comparison between inner and outer leaflet components

Abstract

The physical properties of lipid bilayers with a similar composition to the outer and inner leaflets of the human erythrocyte membrane have been examined in protein-free model systems. The outer leaflet (OL) was represented by a phospholipid mixture containing phosphatidylcholine and sphingomyelin extracted from human erythrocytes, while a mixture of phosphatidylcholine, phosphatidylserine and phosphatidylethanolamine represented the inner leaflet (IL). The ratio of cholesterol to phospholipid was varied in both mixtures. The lateral diffusion coefficient of fluorescent phospholipids diluted in such lipid mixtures was determined by the modulated fringe pattern photobleaching technique. Contrast curves with a single exponential decay, indicative of homogeneous samples, were obtained only for temperatures above 15 degrees C and for a cholesterol to phospholipid molar ratio below 0.8. The rate of lateral diffusion was approximately five times faster in IL than in OL multilayers, in agreement with former results obtained in human erythrocytes (Morrot et al. 1986). Varying the cholesterol to phospholipid ratio from 0 to 0.8 (mol/mol) enabled us to decrease the diffusion constant by only a factor of approximately 2 for both IL and OL mixtures. The order parameter of a spin-labeled phospholipid was determined in the different systems and found to be systematically smaller in IL mixtures than in OL mixtures. The present study indicates that the difference in lipid diffusivity of the two erythrocyte leaflets may be accounted for solely by a difference in phospholipid composition, and may be independent of cholesterol and protein asymmetry.

Phospholipids in animal eukaryotic membranes: transverse asymmetry and movement

“…Similar properties exist also in other cells, such as fibroblasts (El-Hage Chahine et al, 1993). Studies with artificial membranes reconstituted from the characteristic phospholipids of each monolayer demonstrated that differences in microviscosity and diffusibility were primarily due to the phospholipid composition of the membrane (Cribier et al, 1990).…”

Phospholipid transmembrane domains and lateral diffusion in fibroblasts.

“…In a previous publication (14), we have shown that C6-NBD-PtdCho and C6-NBDPtdSer diffuse in egg PtdCho multilayers with the same diffusion coefficient. To verify that the rate of lateral diffusion of the new probe, C6-NBD-SphPCho, is also identical when in the same lipid environment, we compared the lateral diffusion of the latter probe with that of C6-NBD-PtdCho in oriented multilayers composed of egg PtdCho or egg PtdCho and sphingomyelin (50:50, mol/mol).…”

“…Photobleaching of oriented multilayers of egg PtdCho or egg PtdCho/ sphingomyelin (50:50, mol/mol) were carried out as described in Cribier et al. (14).…”

“…In red blood cells, ESR and fluorescence techniques were used to demonstrate a fluidity difference between inner and outer leaflets of the plasma membrane without implying gel formation (11)(12)(13). The difference was attributed to the specific lipid composition of each leaflet, in particular to the greater degree ofunsaturation ofthe lipid chains in the inner monolayer (14).…”

Decoding P4-ATPase substrate interactions

“…Cellular membranes have been shown to display asymmetric differences in membrane fluidity, owing largely to an asymmetric distribution of PL acyl chain composition (Morrot et al , 1986, Cribier et al , 1990, Cribier et al , 1993). These differences are proposed to protect the cell through a tough, exofacial lipid shell of saturated chains, while still providing a malleable, fluid environment of unsaturated chains for the lateral mobility of signaling lipids and the peripheral association of cytosolic proteins (Phillips et al , 2009, Larijani and Poccia, 2012, Czogalla et al , 2014).…”