ABSTRACT
The lipids in one leaflet of an asymmetric artificial lipid vesicle can induce or suppress the formation of ordered lipid domains (rafts) in the opposing leaflet. Whether suppression of domain formation might occur in plasma membranes was studied by using plasma membrane vesicles (PMVs) from RBL-2H3 cells. Ordered domain formation was assessed by FRET and fluorescence anisotropy. Ordered domains in PMV prepared by N-ethyl maleimide (NEM) treatment formed to some extent up to about 37°C. In contrast, ordered domains in symmetric vesicles formed from extracted PMV lipids were stable up to 55°C. This indicates that the stability of ordered domains was substantially less in the intact PMV. A similar decrease in ordered domain stability was observed in artificial asymmetric lipid vesicles relative to the corresponding symmetric vesicles. This suggested either that the intact PMV have a significant degree of lipid asymmetry or that PMV proteins suppress domain formation. Additional experiments ruled out the latter explanation. First, stabilization of ordered domain formation relative to intact PMV was observed in protein-containing symmetric vesicles prepared by detergent solubilization of intact PMV, followed by rapid dilution of detergent. Second, ordered domain stability in intact PMV was not altered after extensively removing PMV proteins with proteinase K. We conclude that intact NEM-induced PMV preserve a significant amount of the lipid asymmetry of plasma membranes, and that loss of PMV lipid asymmetry can induce ordered domain formation, consistent with the possibility that dynamic control of lipid asymmetry can regulate ordered domain formation in the plasma membrane.
Competing Interest Statement
The authors have declared no competing interest.