Role of Aminophospholipids in the Formation of Lipid Rafts in Model Membranes

Abstract

The phase separation of aminophospholipids in glycerophospholipid matrix and the effect of cholesterol were studied by means of fluorescence microscopy of giant unilamellar vesicles (GUV). GUVs were composed of binary mixtures, egg yolk phosphatidylcholine (eggPC)/egg yolk phosphatidylethanolamine (eggPE) and egg yolk phosphatidylcholine (eggPC)/brain phosphatidylserine (brainPS), and ternary ones with both aminophospholipids (eggPC/eggPE/brainPS). Gel/liquid-disordered phase coexistence was detected in these mixtures, where aminophospholipids segregate in gel leaf-like domains. When cholesterol (CHOL) was added, the phase separation was shifted at lower temperatures. CHOL increases miscibility of aminophospholipids in PC matrix. Addition of PE and PS to the ternary mixtures (eggPC/eggSM/CHOL) induced liquid-ordered domain formation at higher temperatures. Based on these results, one can conclude that aminophospholipids promote the formation of Lo domains.

Chip-based sensing for release of unprocessed cell surface proteins in vitro and in serum and its (patho)physiological relevance

“…However, recent studies have demonstrated the expression and functional role of phosphatidylserine at lipid rafts of mammalian plasma membranes. Phosphatidylserine promotes the formation of lipid rafts and low-density liquid-ordered microdomains in physical models of the plasma membranes (22), as well as in plasma membranes of living cells (6), consisting of areas of sphingomyelin in the outer leaflet and PC in concert with phosphatidylserine in the inner leaflet (61). Remarkably, the phospholipid distribution between liquid-ordered raft and liquid-disordered nonraft domains was shown to depend on the method of their isolation, but, with both the detergent-free and the detergent method, phosphatidylserine was recovered with lipid rafts, albeit at rather low concentrations (21).…”

Transverse distribution of plasma membrane bilayer cholesterol: Picking sides

“…Interestingly, the model suggests that in bilayers with outer leaflets rich in sphingolipids and inner leaflets rich in phosphatidylethanolamine, the transverse distribution of cholesterol would vary with its abundance, shifting sharply from outside to inside near the physiologic level in the plasma membrane, ~40 mol%. Supporting this premise is physical evidence that cholesterol strongly interacts with phosphatidylethanolamine at its physiologic plasma membrane concentration . On the other hand, ergosterol does not .…”

“…Supporting this premise is physical evidence that cholesterol strongly interacts with phosphatidylethanolamine at its physiologic plasma membrane concentration. 95,117 On the other hand, ergosterol does not. 95 This challenges the premise that the preponderance of DHE (hence, ergosterol) in the cytoplasmic leaflet of yeast plasma membranes is driven by the phosphatidylethanolamine therein, raising the possibility that another mechanism underlies the inferred ergosterol asymmetry in yeast.…”