Abstract
Fusion of HIV-1 with the membrane of its target cell, an obligate first step in virus infectivity, is mediated by binding of the viral envelope (Env) spike protein to its receptors, CD4 and CCR5/CXCR4, on the cell surface. The process of viral fusion appears to be fast compared with viral egress and has not been visualized by EM. To capture fusion events, the process must be curtailed by trapping Env-receptor binding at an intermediate stage. We have used fusion inhibitors to trap HIV-1 virions attached to target cells by Envs in an extended pre-hairpin intermediate state. Electron tomography revealed HIV-1 virions bound to TZM-bl cells by 2-4 narrow spokes, with slightly more spokes present when evaluated with mutant virions that lacked the Env cytoplasmic tail. These results represent the first direct visualization of the hypothesized pre-hairpin intermediate of HIV-1 Env and improve our understanding of Env-mediated HIV-1 fusion and infection of host cells.
Highlights
The first step of HIV-1 entry into a host target cell, fusion between the viral and target cell membranes, is mediated by the viral envelope spike protein (Env)
Structural studies relevant to understanding Env-mediated membrane fusion include X-ray and single-particle cryo-EM structures of soluble native-like Env trimers in the closed conformation (Ward and Wilson, 2017), CD4-bound open trimers in which the co-receptor binding site on the third hypervariable loop (V3) of gp120 is exposed by V1V2 loop rearrangement (Ozorowski et al, 2017; Wang et al, 2018; Wang et al, 2016; Yang et al, 2019), a gp120 monomeric core-CD4-CCR5 complex (Shaik et al, 2019), and a post-fusion gp41 six-helical bundle formed by an a-helical trimeric coiled coil from the gp41 N-trimer region surrounded by three helices from the C-peptide region (Chan et al, 1997; Weissenhorn et al, 1997; Figure 1a)
The fact that the attachment structure was not found when the viruses and target cells were incubated in the presence of C34, a gp41 N-trimer–targeting C-peptide inhibitor related to T20 (Sougrat et al, 2007), suggests that the rod structure that was trapped during the temperature-arrested state did not involve the pre-hairpin intermediate
Summary
The first step of HIV-1 entry into a host target cell, fusion between the viral and target cell membranes, is mediated by the viral envelope spike protein (Env). HIV-1 Env is a trimeric glycoprotein comprising three gp120 subunits that contain host receptorbinding sites and three gp subunits that include the fusion peptide and membrane-spanning regions. Prior to membrane fusion and formation of the post-fusion gp helical bundle, the viral and host cell membranes are hypothesized to be linked by an extended pre-hairpin intermediate in which insertion of the gp fusion peptide into the host cell membrane exposes the N-trimer (HR1) region of gp
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
