Alanine Scanning Mutagenesis of HIV-1 gp41 Heptad Repeat 1: Insight into the gp120−gp41 Interaction

On the basis of mutagenesis, biochemical, and structural studies, heptad repeat 1 of HIV gp41 (HR1) has been shown to play numerous critical roles in HIV entry, including interacting with gp120 in prefusion states and interacting with gp41 heptad repeat 2 (HR2) in the fusion state. Moreover, HR1 is the site of therapeutic intervention by enfuviritide, a peptide analogue of HR2. In this study, the functional importance of each amino acid residue in gp41 HR1 has been systematically examined by alanine scanning mutagenesis, with subsequent characterization of the mutagenic effects on folding (as measured by incorporation into virions), association with gp120, and membrane fusion. The mutational effects on entry can be grouped into three classes: (1) wild type (defined as >40% of wild-type entry), (2) impaired (defined as 5−40% of wild-type entry), and (3) nonfunctional (defined as <5% of wild-type entry). Interestingly, the majority of HR1 mutations (77%) exhibit impaired or nonfunctional entry. Surprisingly...