Structural characterizations of fusion peptide analogs of influenza virus hemagglutinin. Implication of the necessity of a helix-hinge-helix motif in fusion activity
Journal
Journal of Biological Chemistry
Journal Volume
277
Journal Volume
277
Journal Issue
25
Journal Issue
25
Pages
22725-22733
Start Page
22725
End Page
22733
ISSN
00219258
Date Issued
2002-06-21
Author(s)
Wu, Shih-Hsiung
Chang, Ding-Kwo
Chen, Chinpan
Abstract
Infection by enveloped viruses initially involves membrane fusion between viral and host cell membranes. The fusion peptide plays a crucial role in triggering this reaction. To clarify how the fusion peptide exerts this specific function, we carried out biophysical studies of three fusion peptide analogs of influenza virus hemag-glutinin HA2, namely E5, G13L, and L17A. E5 exhibits an activity similar to the native fusion peptide, whereas G13L and L17A, which are two point mutants of the E5 analog, possess much less fusion activity. Our CD data showed that the conformations of these three analogs in SDS micelles are pH-dependent, with higher α-helical contents at acidic pH. Tryptophan fluorescence emission experiments indicated that these three analogs insert deeper into lipid bilayers at acidic pH. The threedimensional structure of the E5 analog in SDS micelles at pH 4.0 revealed that two segments, Leu2-Glu11 and Trp14-Ile18, form amphipathic helical conformations, with Gly12-Gly13 forming a hinge. The hydrophobic residues in the N- and C-terminal helices form a hydrophobic cluster. At neutral pH, however, the C-terminal helix of Trp14-Ile18 reduces dramatically, and the hydrophobic core observed at acidic pH is severely disrupted. We suggest that the disruption of the C-terminal helix renders the E5 analog fusion-inactive at neutral pH. Furthermore, the decrease of the hinge and the reduction of fusion activity in G13L reveal the importance of the hinge in fusion activity. Also, the decrease in the C-terminal helix and the reduction of fusion activity in L17A demonstrates the importance of the C-terminal helix in fusion activity. Based on these biophysical studies, we propose a model that illustrates the structural change of the HA2 fusion peptide analog and explains how the analog interacts with the lipid bilayer at different pH values.
Type
journal article
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