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

Xiaoyi Wang,Yanxia Chen,Weiliang Xiong,Lu Lu,Xiaochu Ma,Shibo Jiang,Chungen Pan,Asim K Debnath,Meili Wei,Roberto F Speck

doi:10.1371/journal.pone.0044874

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.

Highlights

The fusion of human immunodeficiency virus 1 (HIV-1) and its target cell is mediated by the envelope glycoprotein consisting of surface subunit gp120 and transmembrane subunit gp41 which are associated with non-covalent interactions [1]
The positively charged residue R46 in the HIV-1 gp41 N-terminal heptad repeat (NHR) may participate in formation of a salt bridge with E137 in the C-terminal heptad repeat (CHR) and a hydrogen bond with N43 in the NHR of gp41
The second salt bridge is formed between R46 in the N-terminal portion of the NHR and E137 in the CHR (Figure 1B and Figure 2, Table 1)

Summary

Introduction

The fusion of human immunodeficiency virus 1 (HIV-1) and its target cell is mediated by the envelope glycoprotein consisting of surface subunit gp120 and transmembrane subunit gp which are associated with non-covalent interactions [1]. The gp120 binds to its receptor CD4 on the surface of the target cell and to coreceptors (CCR5 or CXCR4), events which trigger a cascade of conformational changes of gp, facilitating the fusion between membranes of HIV and its target cell [2,3,4]. The HIV-1 gp consists of three major functional domains, including the fusion peptide (FP), the N-terminal heptad repeat (NHR), and the C-terminal heptad repeat (CHR). The peptides derived from the NHR and CHR, e.g., N36 and C34, exhibited potent anti-HIV-1 activity (Figure 1A) [5,6]. The residues at the a and d positions of one NHR domain interact with those at the d and a positions of another NHR domain to form N-

Methods

Results

Conclusion