Membrane structure of the human immunodeficiency virus gp41 fusion domain by molecular dynamics simulation

The structures of the 16-residue fusion domain (or fusion peptide, FP) of the human immunodeficiency virus gp41 fusion protein, two of its mutants, and a shortened peptide (5-16) were studied by molecular dynamics simulation in an explicit palmitoyloleoylphosphoethanolamine bilayer. The simulations showed that the active wild-type FP inserts into the bilayer similar to44degrees +/- 6degrees with respect to the bilayer normal, whereas the inactive V2E and L9R mutants and the inactive 5 to 16 fragment lie on the bilayer surface. This is the first demonstration by explicit molecular dynamics of the oblique insertion of the fusion domain into lipid bilayers, and provides correlation between the mode of insertion and the fusogenic activity of these peptides. The membrane structure of the wild-type FP is remarkably similar to that of the influenza HA(2) FP as determined by nuclear magnetic resonance and electron spin resistance power saturation. The secondary structures of the wild-type FP and the two inactive mutants are quite similar, indicating that the secondary structure of this fusion domain plays little or no role in affecting the fusogenic activity of the fusion peptide. The insertion of the wild-type FP increases the thickness of the interfacial area of the bilayer by disrupting the hydrocarbon chains and extending the interfacial area toward the head group region, an effect that was not observed in the inactive FPs.