PMID:17973492

Citation	Esbjörner, EK, Oglecka, K, Lincoln, P, Gräslund, A and Nordén, B (2007) Membrane binding of pH-sensitive influenza fusion peptides. positioning, configuration, and induced leakage in a lipid vesicle model. Biochemistry 46:13490-504
Abstract	pH-sensitive HA2 fusion peptides from influenza virus hemagglutinin have potential as endosomal escape-inducing components in peptide-based drug delivery. Polarized light spectroscopy and tryptophan fluorescence were used to assess the conformation, orientation, effect on lipid order, and binding kinetics of wild-type peptide HA2(1-23) and a glutamic acid-enriched analogue (INF7) in large unilamellar POPC or POPC/POPG (4:1) lipid vesicles (LUVs). pH-sensitive membrane leakage was established for INF7 but not HA2(1-23) using an entrapped-dye assay. A correlation is indicated between leakage and a low degree of lipid chain order (assessed by linear dichroism, LD, of the membrane orientation probe retinoic acid). Both peptides display poor alignment in zwitterionic POPC LUVs compared to POPC/POPG (4:1) LUVs, and it was found that peptide-lipid interactions display slow kinetics (hours), resulting in reduced lipid order and increased tryptophan shielding. At pH 7.4, INF7 displays tryptophan emission and LD features indicative of a surface-orientated peptide, suggesting that its N-terminal glutamic acid residues prevent deep penetration into the hydrocarbon core. At pH 5.0, INF7 displays weaker LD signals, indicating poor orientation, possibly due to aggregation. By contrast, the orientation of the HA2(1-23) peptide backbone supports previously reported oblique insertion ( approximately 60-65 degrees relative to the membrane normal), and aromatic side-chain orientations are consistent with an interfacial (pH-independent) location of the C-terminus. We propose that a conformational change upon reduction of pH is limited to minor rearrangements of the peptide "hinge region" around Trp14 and repositioning of this residue.
Links	PubMed Online version:10.1021/bi701075y
Keywords	Amino Acid Sequence; Binding Sites; Circular Dichroism; Hemagglutinin Glycoproteins, Influenza Virus/chemistry; Hemagglutinin Glycoproteins, Influenza Virus/metabolism; Hydrogen-Ion Concentration; Magnetic Resonance Spectroscopy; Membrane Fusion; Models, Biological; Models, Molecular; Molecular Sequence Data; Peptide Fragments/chemistry; Peptide Fragments/metabolism; Peptides/chemistry; Peptides/metabolism; Phosphatidylcholines/chemistry; Protein Conformation; Spectrometry, Fluorescence; Tryptophan/chemistry; Tryptophan/metabolism; Unilamellar Liposomes/chemistry; Unilamellar Liposomes/metabolism
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