The Conserved Residue Arg46 in the N-Terminal Heptad Repeat Domain of HIV-1 gp41 Is Critical for Viral Fusion and Entry

Abstract

During the process of HIV-1 fusion with the target cell, the N-terminal heptad repeat (NHR) of gp41 interacts with the C-terminal heptad repeat (CHR) to form fusogenic six-helix bundle (6-HB) core. We previously identified a crucial residue for 6-HB formation and virus entry - Lys63 (K63) in the C-terminal region of NHR (aa 54–70), which forms a hydrophobic cavity. It can form an important salt bridge with Asp121 (D121) in gp41 CHR. Here, we found another important conserved residue for virus fusion and entry, Arg46 (R46), in the N-terminal region of NHR (aa 35–53), which forms a hydrogen bond with a polar residue, Asn43 (N43), in NHR, as a part of the hydrogen-bond network. R46 can also form a salt bridge with a negatively charged residue, Glu137 (E137), in gp41 CHR. Substitution of R46 with the hydrophobic residue Ala (R46A) or the negatively charged residue Glu (R46E) resulted in disruption of the hydrogen bond network, breakage of the salt bridge and reduction of 6-HB’s stability, leading to impairment of viral fusion and decreased inhibition of N36, an NHR peptide. Similarly, CHR peptide C34 with substitution of E137 for Ala (E137A) or Arg (E137R) also exhibited reduced inhibitory activity against HIV-1 infection and HIV-1-mediated cell-to-cell fusion. These results suggest that the positively charged residue R46 and its hydrogen bond network, together with the salt bridge between R46 and E137, are important for viral fusion and entry and may therefore serve as a target for designing novel HIV fusion/entry inhibitors.

Measures for diagnosing and treating infections by a novel coronavirus responsible for a pneumonia outbreak originating in Wuhan, China

“…S1 determines the virus host range and cellular tropism with the key functional domain -receptor binding domain (RBD), while S2 contains two tandem domains, heptad repeats 1 (HR1) and heptad repeats 2 (HR2), to mediate virus-cell membrane fusion. It is believed that the fusion process is similar to that of HIV-1 [28]; for example, when S1 binds to the receptor on the cell membrane, the fusion peptide at the N terminus of S2 inserts into the cell membrane, then three HR1s attach to each other in parallel as a trimer, followed by binding of three HR2s separately onto the outside of the trimer to form a 6-helix bundle, thus bringing virus and cell membranes close to each other to trigger fusion.…”

Heptad stereotypy, S/Q layering, and remote origin of the SARS-CoV-2 fusion core

“… He et al. 2007 ; Wang et al. 2012 ) and that, instead, the FC/HR regions are not among the most prominent antibody targets in the spike protein (e.g.…”

Structure of transmembrane subunits gp47 of the foamy virus envelope glycoproteins

“…Th e HRs, which were linked by the β-strands and loops region, would assist the N-terminal FP and the C-terminal MPER during membrane merging. It had been proposed that the HRs of infl uenza HA2, HIV-1/SIV gp41, Ebola virus GP2 and Simian virus 5 F1 were able to form six-helix bundles in a post-fusion form (Chan et al, 1997;Malashkevich, 1999;Yueyong et al, 2006;Wang et al, 2012). For FVs gp47, a six-helix bundle could also been formed, in which three N-HRs formed an interior N-helix trimer, and three C-HRs inserted into the highly conserved, hydrophobic cavities on the surface.…”