Atomic structure of a thermostable subdomain of HIV-1 gp41

Abstract

Infection by HIV-1 involves the fusion of viral and cellular membranes with subsequent transfer of viral genetic material into the cell. The HIV-1 envelope glycoprotein that mediates fusion consists of the surface subunit gp120 and the transmembrane subunit gp41. gp120 directs virion attachment to the cell-surface receptors, and gp41 then promotes viral-cell membrane fusion. A soluble, ␣-helical, trimeric complex within gp41 composed of N-terminal and C-terminal extraviral segments has been proposed to represent the core of the fusion-active conformation of the HIV-1 envelope. A thermostable subdomain denoted N34(L6)C28 can be formed by the N-34 and C-28 peptides connected by a f lexible linker in place of the disulfide-bonded loop region. Threedimensional structure of N34(L6)C28 reveals that three molecules fold into a six-stranded helical bundle. Three Nterminal helices within the bundle form a central, parallel, trimeric coiled coil, whereas three C-terminal helices pack in the reverse direction into three hydrophobic grooves on the surface of the N-terminal trimer. This thermostable subdomain displays the salient features of the core structure of the isolated gp41 subunit and thus provides a possible target for therapeutics designed selectively to block HIV-1 entry.

Surface Exposure of the HIV-1 Env Cytoplasmic Tail LLP2 Domain during the Membrane Fusion Process

“…4 The abbreviations used are: HIV, human immunodeficiency virus; HIV-1, HIV type 1; CT, cytoplasmic tail; NHR, N-terminal heptad repeat; CHR, C-terminal heptad repeat; ELISA, enzyme-linked immunosorbent assay; FITC, fluorescein isothiocyanate; SPR, surface plasmon resonance; TBS, Tris buffered solution; GMEM, glutamine-deficient minimal essential medium; 6-HB, six-helix bundle; mAb, monoclonal antibody; aa, amino acid.…”

“…It is generally agreed that the human immunodeficiency virus (HIV) 4 envelope glycoprotein (Env) transmembrane subunit gp41 plays an essential role during viral infection by mediating membrane fusion. Based on the crystal structure of the gp41 core, Chan et al (1,2) have proposed a membrane fusion model for HIV-1 entry.…”

“…In this model, the Env surface subunit gp120 binds to both CD4 and the chemokine receptor (CCR5 or CXCR4) on the target cells to trigger a conformational change of gp41, i.e. association between its N-and C-terminal heptad repeats (NHR and CHR, respectively) to form a six-helix bundle (6-HB), which is thought to bring the membranes of both virus and target cells into close proximity for facilitating membrane fusion (1,(3)(4)(5)(6). However, the events following 6-HB formation prior to completion of the fusion process are unclear, and the regulation of the fusion process remains to be elucidated.…”

Role of the Envelope Genetic Context in the Development of Enfuvirtide Resistance in Human Immunodeficiency Virus Type 1-Infected Patients

“…Like most of the retroviral transmembrane proteins, the ectodomain of gp41 contains an N-terminal fusion peptide followed by two heptad repeat domains (HR1 and HR2), which are connected by a non-helical loop region of 25 to 30 amino acids. Membrane fusion is currently thought to result from the insertion of the fusion peptide into the cellular membrane, and the formation of a six-helix bundle in which the central trimeric HR1 coiled-coil forms three hydrophobic grooves onto which three HR2 domains pack in reverse orientation (4,5,40,43).…”

“…Like most of the retroviral transmembrane proteins, the ectodomain of gp41 contains an N-terminal fusion peptide followed by two heptad repeat domains (HR1 and HR2), which are connected by a non-helical loop region of 25 to 30 amino acids. Membrane fusion is currently thought to result from the insertion of the fusion peptide into the cellular membrane, and the formation of a six-helix bundle in which the central trimeric HR1 coiled-coil forms three hydrophobic grooves onto which three HR2 domains pack in reverse orientation (4,5,40,43).Although several HIV-1 entry inhibitors have been evaluated in clinical trials and have shown promising prospects for therapy (1, 28), the only entry inhibitor licensed to date is the fusion inhibitor enfuvirtide (ENF; also called T20), which has shown potent antiviral activity in patients, resulting in sustained viral load reduction when used in combination with an optimized background regimen of protease and/or reverse transcriptase inhibitors (21-23). Similar to results with other antiviral agents, however, ENF-resistant HIV-1 variants may emerge under the selective pressure of ENF (26,32,39,42) whenever the treatment fails to completely suppress viral replication in vivo.…”