Surface potential regulation of phospholipid composition and in‐out translocation in yeast

Abstract

In yeast cells the anionic phospholipids, phosphatidylinositol and phosphatidylserine, determine to a large extent the magnitude of the negative surface charge density (a) [Cerbon, J. & Calderon, V, (1990) Biochim. Biophys. Acta 1028, 261-2671. We now report further findings. (a) When the yeast qoUt was reduced by increasing the concentration of monovalent (C') or divalent (C"+) cations in the culture medium, the relative amount of anionic phospholipids increased (45-52%). (b) For each such increment, a corresponding increase in the external surface charge density (a) was found, due to the translocation from the cytoplasmic side to the exoplasmic side of the plasma membrane. (c) These changes were reversed when the yl""' was increased by reducing the concentration of cations in the culture medium. (d) When the yo"' was reduced and phosphatidylserine decarboxylation or phosphatidylinositol degradation were inhibited, to measure synthesis of anionic phospholipids, a 1.4 times further increase in the anionic/zwitterionic phospholipid ratio occurred. As a consequence, a similar increase in the external surface charge (0) was found. (e) Under all the conditions studied, the percentage of anionic phospholipid at the external surface of the plasma membrane calculated from the a values was 2.3-3.0 times less than that in the cells, indicating that the asymmetric composition (more inside) was maintained. A model for the regulation of the anionic phospholipid composition of the yeast membranes is proposed.The genetics and biochemistry of phospholipid biosynthesis have been extensively studied in Escherichia coli [1] and in the yeast Saccharomyces cerevisiae [2]. Many of the enzymes of phospholipid biosynthesis are known to be activated by lipids and/or detergents and, in general, anionic lipids are better activators than neutral lipids [3]. The lipid dependence of these enzymes is of considerable interest, not only in the context of the general implications for lipidprotein interactions, but in view of the dual role of lipid molecules as subswate/products and modulators of activity. We have shown that anionic-phospholipid-rich cells have an increased surface potential (9""') which activates the highaffinity H-linked transport systems and inhibits the transport of anions from high external concentrations [4]. The activity of these membrane proteins ( K , and optimum pH) was regulated by the anionic phospholipids through their effects upon membrane electrostatics. Also, these changes in the membrane phospholipid composition modify their asymmetric distribution [5]. Taking into account that most phospholipid biosynthetic enzymes are membrane proteins, and that membrane phospholipid composition is one of the observed regulatory mechanisms in vitro [2], the effect of varying the external surface potential (@'"') upon the phospholipid composition and distribution in normal PtdIns-rich and PtdSer-rich cells was studied. The cell's pot'' was increased or decreased by altering the concentration of monovalent (NaC1) or divalent (M...

Partitioning of a-Factor Analogues into Membranes: Analysis of Binding and Importance for Biological Activity

“…Values of K p and the charge density of the yeast membranes obtained from the curve-fitting procedure were (8 ( 6) × 10 5 and -0.02 ( 0.01 C m -2 , respectively. The charge density of the yeast membranes obtained from the curvefitting procedure is in good agreement with values obtained by others using an unrelated membrane probe (Cerbon & Calderon, 1994). The partition coefficient of the yeast membranes is within experimental error of the partition coefficient determined from experiments with synthetic vesicles (Tables 1 and 3).…”

Comparison of the Membrane Interaction and Permeabilization by the Designed Peptide Ac-MB21-NH2 and Truncated Dermaseptin S3

“…These lipids are abundantly present in the outer leaflet of the cytoplasmic membrane of bacteria, explaining the high activity against these organisms. In yeast plasma membranes, about 25-30% of the anionic lipids are present in the outer leaflet (12). Mammalian cells generally do not expose anionic lipids in the outer leaflet of their plasma membrane and are not or hardly susceptible to cationic peptides.…”

Rapid transbilayer movement of fluorescent phospholipid analogues in the plasma membrane of endocytosis‐deficient yeast cells does not require the Drs2 protein

“…Therefore, these data do not support the suggestion that the Drs2 protein has (aminophospholipid) translocase activity which could be responsible for maintaining the asymmetric distribution of endogenous phospholipids as in mammalian plasma membranes. Thus, other membrane proteins not as yet identified and/or, as previously suggested, the surface potential of the plasma membrane should be considered [19].…”

“…Different mechanisms have been suggested to be responsible for the origin and maintenance of this asymmetry. Cerbón and Calderón [19] concluded that surface potential is strongly involved in the regulation of phospholipid asymmetry. Recent studies have demonstrated that transbilayer movement of lipids in the plasma membrane of S. cerevisiae is protein‐mediated [13,20–22], suggesting that the lipid asymmetry in S. cerevisiae could be protein‐controlled also.…”