Fusion activity of an amphiphilic polypeptide having acidic amino acid residues: generation of fusion activity by alpha-helix formation and charge neutralization.
A sequential polypeptide, poly(Glu-Aib-Leu-Aib) (Aib represents 2-aminoisobutyric acid), was synthesized and the pH-dependence of fusogenic activity of the polypeptide was studied. The polypeptide was designed to take amphiphilic structure upon the formation of alpha-helix. Circular dichroism spectra of the polypeptide showed a negative Cotton effect with double minima, indicative of an alpha-helical conformation. The alpha-helix content was increased with lowering pH and/or increasing the ionic strength. It was found that the polypeptide induces remarkable leakage of calcein from egg-yolk phosphatidylcholine (EYPC) vesicles loaded in the inner aqueous phase with lowering pH and/or increasing ionic strength. The polypeptide caused fusion of EYPC liposomes and dipalmitoylphosphatidylcholine liposomes more strongly with decreasing pH. Moreover, two distinct increases of fusogenic activity of the polypeptide were observed near pH 6.0 and below pH 4.5. The former corresponds to the midpoint of pH-dependent change in helical content of the polypeptide and the latter the pKa of the gamma-carboxyl group of glutamic acid. These results indicate that elevation of the fusogenic activity of the polypeptide is related to the increase in two factors, alpha-helix content and hydrophobicity.
Department of Applied Chemistry, College of Engineering, University of Osaka Prefecture, Japan.
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Kono
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Nishii
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Takagishi
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry*; D005452:Fluoresceins; D006863:Hydrogen-Ion Concentration; D008051:Lipid Bilayers / Q000737:chemistry*; D008081:Liposomes; D008561:Membrane Fusion; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D009500:Neutralization Tests; D009994:Osmolar Concentration; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry*; D010713:Phosphatidylcholines
D000596:Amino Acids; D005452:Fluoresceins; D008051:Lipid Bilayers; D008081:Liposomes; D010455:Peptides; D010713:Phosphatidylcholines; C007740:fluorexon