Download MendeleyIntermediate conformations of CD4-bound HIV-1 Env heterotrimers.
Dam, K.A., Fan, C., Yang, Z., Bjorkman, P.J.(2023) Nature 623: 1017-1025
- PubMed: 37993719
- DOI: https://doi.org/10.1038/s41586-023-06639-8
- Primary Citation of Related Structures:
8FYI, 8FYJ - PubMed Abstract:
HIV-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.
Organizational Affiliation:
Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA.
