Temperature dependence, structural plasticity, and resonance assignment of uniformly labeled HIV-1 fusion peptides associated with membranes

The HIV-1 viral fusion peptide serves as a biologically relevant model for viral/target cell membrane fusion and in my work, the structure of the membrane-associated peptide was probed by solid state NMR MAS 13C chemical shift measurements. Solution NMR studies have shown that the peptide is predominantly helical in detergent micelles and this was correlated with solid state NMR 13C chemical shifts in frozen detergent. Large shift changes (2–4 ppm) were observed for the peptide in a mixture whose lipid headgroup and cholesterol composition reflects the membranes of host cells of the virus. In this more biologically relevant composition, the chemical shifts are consistent with predominant non-helical structure. NMR spectra were compared at −50°C and at 20°C. Similar peak chemical shifts were observed at both temperatures, which indicates that cooling the sample does not significantly change the peptide structure. Relative to −50°C, the 20°C signals were narrower and had lower intensity, which is consistent with greater motion at higher temperature. 13C/13C correlation experiments were performed on a sample in which the peptide was U-13C/15N labeled over three or twelve sequential residues. The resulting 2D spectra were used to assign the 13C chemical shifts in the labeled residues and the shifts were consistent with beta strand structure. 15N-13C correlation experiments were also done on a uniformly 13C/15N N-Acetyl-leucine model compound sample.