Functional and Structural Measurements of HIV gp41 Fusion Protein Constructs

Abstract

The initial step of HIV infection is fusion between the viral and target cell membranes. Fusion is mediated by the HIV gp41 protein and its N-terminal “fusion peptide” (FP) which binds to target cell membranes. Shorter constructs of gp41 that contain the FP usually catalyze vesicle fusion and such fusion at physiological pH was measured for three different gp41 constructs which differed in their numbers of N-terminal gp41 residues. “FP34” and “N70” were respectively models of the FP and “pre-hairpin intermediate” gp41 conformation while “FP-hairpin” was a model of the final “six-helix-bundle” gp41 structure. N70 induced rapid fusion, FP34 induced moderate fusion, and FP-hairpin induced no fusion and even arrested fusion induced by FP34. The data therefore suggest that the six-helix bundle conformation stops membrane fusion. In related work, solid-state nuclear magnetic resonance measurements probed the membrane locations of three different FP constructs with very different fusion rates. There was a positive correlation between fusion rate and depth of membrane insertion for the FP in either helical or β strand conformation. The key determinant of fusion rate may therefore be FP membrane location rather than conformation.View Large Image | View Hi-Res Image | Download PowerPoint Slide