High-Resolution Secondary and Tertiary Structure of the Membrane-Associated HIV Fusion Peptide by Itself and in Large gp41 Ectodomain Constructs: Correlation Between Beta Sheet Registry, Membrane Insertion and Perturbation, and Fusion Catalysis

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. The FP by itself catalyzes membrane fusion and the secondary and tertiary structure of membrane-associated FP was probed at high-resolution using solid-state NMR spectroscopy. For membranes with biologically-relevant cholesterol content, the FP forms antiparallel β sheet structure with a wide distribution of antiparallel registries. The population of each registry was quantified and a good correlation was observed between registries that were populated and those which had negative free energies of membrane insertion. A very different registry distribution was detected for the non-functional V2E mutant which binds to membranes but is not membrane-inserted. These results support a general structure-function model which correlates β sheet FP registry, FP membrane insertion and membrane perturbation, and fusion catalysis. This model is currently being tested for large membrane-associated ectodomain constructs of gp41 that contain the FP.