Solid-State NMR Spectroscopy of Human Immunodeficiency Virus Fusion Peptides Associated with Host-Cell-Like Membranes: 2D Correlation Spectra and Distance Measurements Support a Fully Extended Conformation and Models for Specific Antiparallel Strand Registries
Wei Qiang, Michele L. Bodner, and David P. Weliky*
The human immunodeficiency virus (HIV) is “enveloped” by a membrane, and infection of a host cell begins with fusion between viral and target cell membranes. Fusion is catalyzed by the HIV gp41 protein which contains a functionally critical ~20-residue apolar “fusion peptide” (HFP) that associates with target cell membranes. In this study, chemically synthesized HFPs were associated with host-cell-like membranes and had “scatter-uniform” labeling (SUL), that is, only one residue of each amino acid type was U−13C, 15N labeled. For the first sixteen HFP residues, an unambiguous 13C chemical shift assignment was derived from 2D 13C/13C correlation spectra with short mixing times, and the shifts were consistent with continuous β-strand conformation. 13C−13C contacts between residues on adjacent strands were derived from correlation spectra with long mixing times and suggested close proximity of the following residues: Ala-6/Gly-10, Ala-6/Phe-11, and Ile-4/Gly-13. Specific antiparallel β-strand registries were further tested using a set of HFPs that were 13CO-labeled at Ala-14 and 15N-labeled at either Val-2, Gly-3, Ile-4, or Gly-5. The solid-state NMR data were fit with 50–60% population of antiparallel HFP with either Ala-14/Gly-3 or Ala-14/Ile-4 registries and 40–50% population of structures not specified by the NMR experiments. The first two registries correlated with intermolecular hydrogen bonding of 15–16 apolar N-terminal residues and this hydrogen-bonding pattern would be consistent with a predominant location of these residues in the hydrophobic membrane interior. To our knowledge, these results provide the first residue-specific structural models for membrane-associated HFP in its β-strand conformation.