Structural highlights
Function
[B2YFS0_9HIV1] Envelope glycoprotein gp160: Oligomerizes in the host endoplasmic reticulum into predominantly trimers. In a second time, gp160 transits in the host Golgi, where glycosylation is completed. The precursor is then proteolytically cleaved in the trans-Golgi and thereby activated by cellular furin or furin-like proteases to produce gp120 and gp41.[HAMAP-Rule:MF_04083] Surface protein gp120: Attaches the virus to the host lymphoid cell by binding to the primary receptor CD4. This interaction induces a structural rearrangement creating a high affinity binding site for a chemokine coreceptor like CXCR4 and/or CCR5. Acts as a ligand for CD209/DC-SIGN and CLEC4M/DC-SIGNR, which are respectively found on dendritic cells (DCs), and on endothelial cells of liver sinusoids and lymph node sinuses. These interactions allow capture of viral particles at mucosal surfaces by these cells and subsequent transmission to permissive cells. HIV subverts the migration properties of dendritic cells to gain access to CD4+ T-cells in lymph nodes. Virus transmission to permissive T-cells occurs either in trans (without DCs infection, through viral capture and transmission), or in cis (following DCs productive infection, through the usual CD4-gp120 interaction), thereby inducing a robust infection. In trans infection, bound virions remain infectious over days and it is proposed that they are not degraded, but protected in non-lysosomal acidic organelles within the DCs close to the cell membrane thus contributing to the viral infectious potential during DCs' migration from the periphery to the lymphoid tissues. On arrival at lymphoid tissues, intact virions recycle back to DCs' cell surface allowing virus transmission to CD4+ T-cells.[HAMAP-Rule:MF_04083] Transmembrane protein gp41: Acts as a class I viral fusion protein. Under the current model, the protein has at least 3 conformational states: pre-fusion native state, pre-hairpin intermediate state, and post-fusion hairpin state. During fusion of viral and target intracellular membranes, the coiled coil regions (heptad repeats) assume a trimer-of-hairpins structure, positioning the fusion peptide in close proximity to the C-terminal region of the ectodomain. The formation of this structure appears to drive apposition and subsequent fusion of viral and target cell membranes. Complete fusion occurs in host cell endosomes and is dynamin-dependent, however some lipid transfer might occur at the plasma membrane. The virus undergoes clathrin-dependent internalization long before endosomal fusion, thus minimizing the surface exposure of conserved viral epitopes during fusion and reducing the efficacy of inhibitors targeting these epitopes. Membranes fusion leads to delivery of the nucleocapsid into the cytoplasm.[HAMAP-Rule:MF_04083]
Publication Abstract from PubMed
Understanding the mechanisms used by HIV-1 to evade antibody neutralization may contribute to the design of a high-coverage vaccine. The tier 3 virus 253-11, is poorly neutralized by subtype-matched and subtype C sera, even when compared to other tier 3 viruses, and is also recognized poorly by V3/glycan targeting monoclonal antibodies. We found that sequence polymorphism in the V3 loop and N-linked glycosylation sites only minimally contribute to the high neutralization resistance of 253-11. Interestingly, the 253-11 membrane proximal external region (MPER) is rarely recognized by sera in the context of the wild-type virus, but is commonly recognized in the context of an HIV-2 chimeric virus, suggesting steric or kinetic hindrance of binding to MPER in the native Env. Mutations in the 253-11 MPER - which were previously reported to increase the lifetime of the pre-fusion Envelope (Env) conformation - affected the resistance of 253-11 to antibodies targeting various epitopes on HIV-1 Env, presumably destabilizing its otherwise stable, closed trimer structure. To gain insight into the structure of 253-11, we constructed and crystallized a recombinant 253-11 SOSIP trimer. The resulting structure revealed that the heptad repeat helices in gp41 are drawn in close proximity to the trimer axis and that gp120 protomers also showed a relatively compact disposition around the trimer axis. These observations give substantial insight into the molecular features of an envelope spike from a tier 3 virus and into possible mechanisms that may contribute to its unusually high neutralization resistance.IMPORTANCE HIV-1 isolates that are highly resistant to broadly neutralizing antibodies could limit the efficacy of an antibody-based vaccine. We studied 253-11, which is highly resistant to commonly-elicited neutralizing antibodies. To further understand its resistance, we made mutations that are known to delay fusion and thus increase the time the virus spends in the open conformation following CD4-binding. Interestingly, we found that these mutations affect the 253-11 Envelope (Env) spike before CD4 binding, presumably by destabilizing the trimer structure. To gain further information about the structure of the 253-11 Env trimer, we generated a recombinant 253-11 SOSIP trimer. The crystal structure of the SOSIP trimer revealed that the gp41 helices and the gp120 protomers were drawn in towards the center of the molecule compared to most solved HIV-1 Env structures. These observations provide insight into the distinct molecular features of a Tier 3 envelope spike.
Molecular basis of unusually high neutralization resistance in tier 3 HIV-1 strain 253-11.,Moyo T, Ereno-Orbea J, Jacob RA, Pavillet CE, Kariuki SM, Tangie EN, Julien JP, Dorfman JR J Virol. 2018 Apr 4. pii: JVI.02261-17. doi: 10.1128/JVI.02261-17. PMID:29618644[1]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
See Also
References
- ↑ Moyo T, Ereno-Orbea J, Jacob RA, Pavillet CE, Kariuki SM, Tangie EN, Julien JP, Dorfman JR. Molecular basis of unusually high neutralization resistance in tier 3 HIV-1 strain 253-11. J Virol. 2018 Apr 4. pii: JVI.02261-17. doi: 10.1128/JVI.02261-17. PMID:29618644 doi:http://dx.doi.org/10.1128/JVI.02261-17
