n-methyl-1-2-dioleoylphosphatidylethanolamine and 1-2-dielaidoylphosphatidylethanolamine

We have studied the interaction between phospholipids and a-factor (YIIKGVFWDPAC-[Farn]OMe), S-alkylated forms of a-factor with the farnesyl group substituted by methyl, hexadecanyl, or benzyl groups, and truncated forms of this lipopeptide. Circular dichroism studies suggest that, despite its lack of farnesylation, S-methyl-a-factor is incorporated into vesicles of dimyristoylphosphatidylcholine in a conformation similar to that which a-factor adopts in this membrane. However, studies of the intrinsic fluorescence of the Trp residues of these peptides indicate that this residue is more deeply imbedded into the bilayer in the case of the farnesylated peptide. The a-factor is more effective in raising the bilayer to the hexagonal phase transition temperature of dielaidoylphosphatidylethanolamine than is the S-methyl-a-factor. This bilayer-stabilizing ability is also reflected in a-factor inhibiting leakage from vesicles of N-methyldioleoylphosphatidylethanolamine. Studies on a-factor analogs permit the conclusion that the bilayer-stabilizing effect of a-factor is not solely a consequence of its greater partitioning into the membrane but is also a consequence of the degree of penetration into the bilayer and the specific conformation of the peptide at the membrane interface. These results indicate that the farnesyl group alone, in the absence of cellular factors, bestows a particular physical interaction with membranes.

Topics: Amino Acid Sequence; Circular Dichroism; Dimyristoylphosphatidylcholine; Lipid Bilayers; Magnetic Resonance Spectroscopy; Mating Factor; Methylation; Molecular Sequence Data; Peptides; Phosphatidylethanolamines; Phospholipids; Protein Conformation; Protein Prenylation; Spectrometry, Fluorescence

The peptide ZfFG is known to inhibit non-bilayer phase formation as well as vesicle-vesicle and viral fusion. In order to ascertain some of the properties or structural features of this peptide which were important for the inhibition of membrane fusion, the blocking group was transferred from the amino to the carboxyl end to make fFGOBz. The fFGOBz lowered the bilayer to hexagonal phase transition temperature of dielaidoylphosphatidylethanolamine and it promoted the formation of isotropic phases in monomethyldioleoylphosphatidylethanolamine. The promotion of non-bilayer phases by fFGOBz appeared to be enhanced by a charged terminal amino group as higher pH or formylation of the amino group both decreased the effectiveness of this peptide to induce formation of the hexagonal phase. With the monomethyldioleoylphosphatidylethanolamine, the fFGOBz also promoted vesicle leakage and fusion as measured by lipid intermixing. The fFGOBz did not inhibit the formation of lipid structures of high curvature, resulting from sonication of phosphatidylcholine, as did ZfFG. Thus, the effects of fFGOBz on membranes are in sharp contrast to those of ZfFG and more closely resemble the behaviour of larger fusion peptides corresponding to the amino-terminal segment of viral fusion proteins. Our results demonstrate that having the carbobenzoxy group on the amino-terminus of fFG is important for giving the peptide derivative the property of inhibiting membrane fusion.

Topics: Amino Acid Sequence; Calorimetry, Differential Scanning; Hydrogen-Ion Concentration; Lipid Bilayers; Magnetic Resonance Spectroscopy; Membrane Fusion; Models, Biological; Molecular Sequence Data; Oligopeptides; Phosphatidylethanolamines; Sonication; Temperature; Viral Fusion Proteins