Nuclear magnetic resonance evidence for retention of a lamellar membrane phase with curvature in the presence of large quantities of the HIV fusion peptide

The HIV fusion peptide (HFP) is a biologically relevant model system to understand virus/host cell fusion. 2H and 31P NMR spectroscopies were applied to probe the structure and motion of membranes with bound HFP and with a lipid headgroup and cholesterol composition comparable to that of membranes of host cells of HIV. The lamellar phase was retained for a variety of highly fusogenic HFP constructs as well as a non-fusogenic HFP construct and for the influenza virus fusion peptide. The lamellar phase is therefore a reasonable structure for modeling the location of HFP in lipid/cholesterol dispersions. Relative to no HFP, membrane dispersions with HFP had faster 31P transverse relaxation and faster transverse relaxation of acyl chain 2H nuclei closest to the lipid headgroups. Relative to no HFP, mechanically aligned membrane samples with HFP had broader 31P signals with a larger fraction of unoriented membrane. The relaxation and aligned sample data are consistent with bilayer curvature induced by the HFP which may be related to its fusion catalytic function. In some contrast to the subtle effects of HFP on a host-cell-like membrane composition, an isotropic phase was observed in dispersions rich in phosphatidylethanolamine lipids and with bound HFP.