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Structure of HIV-1 BG505 SOSIP-HT1 in complex with one CD4 molecule
Structural highlights
FunctionQ2N0S5_9HIV1 The envelope glyprotein gp160 precursor down-modulates cell surface CD4 antigen by interacting with it in the endoplasmic reticulum and blocking its transport to the cell surface.[RuleBase:RU004292][SAAS:SAAS00139820] The gp120-gp41 heterodimer allows rapid transcytosis of the virus through CD4 negative cells such as simple epithelial monolayers of the intestinal, rectal and endocervical epithelial barriers. Both gp120 and gp41 specifically recognize glycosphingolipids galactosyl-ceramide (GalCer) or 3' sulfo-galactosyl-ceramide (GalS) present in the lipid rafts structures of epithelial cells. Binding to these alternative receptors allows the rapid transcytosis of the virus through the epithelial cells. This transcytotic vesicle-mediated transport of virions from the apical side to the basolateral side of the epithelial cells does not involve infection of the cells themselves.[SAAS:SAAS00140087] Publication Abstract from PubMedHIV-1 envelope (Env) exhibits distinct conformational changes in response to host receptor (CD4) engagement. Env, a trimer of gp120 and gp41 heterodimers, has been structurally characterized in a closed, prefusion conformation with closely associated gp120s and coreceptor binding sites on gp120 V3 hidden by V1V2 loops(1-4) and in fully saturated CD4-bound open Env conformations with changes including outwardly rotated gp120s and displaced V1V2 loops(3-9). To investigate changes resulting from substoichiometric CD4 binding, we solved single-particle cryo-electron microscopy (cryo-EM) structures of soluble, native-like heterotrimeric Envs bound to one or two CD4 molecules. Most of the Env trimers bound to one CD4 adopted the closed, prefusion Env state, with a minority exhibiting a heterogeneous partially open Env conformation. When bound to two CD4s, the CD4-bound gp120s exhibited an open Env conformation including a four-stranded gp120 bridging sheet and displaced gp120 V1V2 loops that expose the coreceptor sites on V3. The third gp120 adopted an intermediate, occluded-open state(10) that showed gp120 outward rotation but maintained the prefusion three-stranded gp120 bridging sheet with only partial V1V2 displacement and V3 exposure. We conclude that most of the engagements with one CD4 molecule were insufficient to stimulate CD4-induced conformational changes, whereas binding two CD4 molecules led to Env opening in CD4-bound protomers only. The substoichiometric CD4-bound soluble Env heterotrimer structures resembled counterparts derived from a cryo-electron tomography study of complexes between virion-bound Envs and membrane-anchored CD4 (ref. (11)), validating their physiological relevance. Together, these results illuminate intermediate conformations of HIV-1 Env and illustrate its structural plasticity. Intermediate conformations of CD4-bound HIV-1 Env heterotrimers.,Dam KA, Fan C, Yang Z, Bjorkman PJ Nature. 2023 Nov;623(7989):1017-1025. doi: 10.1038/s41586-023-06639-8. Epub 2023 , Nov 22. PMID:37993719[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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