P-C18 HIV-1 Env Adopts an Open Trimer Conformation in Response to Fusion Inhibitor Resistance

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Peptide entry inhibitors block HIV entry by inhibiting membrane fusion with the target host cell. They are made up of short peptide analogs of either the N- or C-terminal heptad repeats (HRs) of gp41. These peptides act by direct binding to a gp41 fusion intermediate and preventing formation of the 6-helix bundle that drives virus-host cell membrane fusion. Previously, our group reported on 2 genetically distinct pathways of N-terminal peptide resistance mutation, defined by founding mutations in either the N- or C-terminal HRs—pathway 1 and pathway 2, respectively. While peptide resistance maps to gp41 mutations, both pathways include non-overlapping sets of secondary mutations in gp120, suggesting distinct routes of crosstalk between gp41 and gp120. Using a lentiviral pseudovirus system, we have evaluated the infectivity, sensitivity to nAbs, sCD4, and temperature sensitivity of Envs from both fusion inhibitor resistance pathways. Envs from both pathways adopt an “open” trimer conformation, becoming more sensitive to sCD4, weakly neutralizing and non-neutralizing antibodies, while becoming more resistant to a subset of bNAbs preferring the native/closed trimer conformation. In most cases, changes in neutralization sensitivity map to Gp120 mutations. Our analysis reveals the 2 pathways are not equivalent, involving distinct sets of changes in both Gp120 and Gp41. Pathway 1 Envs are more sensitive to sCD4 than WT and Pathway 2 Envs, and exhibit greater neutralization sensitivity in general, suggesting a more open conformation or greater degree of conformational flexibility. Efforts are underway to understand the mechanism of these changes in the context of viral entry.

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