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. Author manuscript; available in PMC: 2022 Oct 1.
Published in final edited form as: Curr Opin Virol. 2021 Aug 12;50:59–68. doi: 10.1016/j.coviro.2021.07.005

Figure 1. Conformational dynamics of the Env trimer.

Figure 1.

smFRET imaging revealed three conformational states of Env protomers (State 1, State 2, and State 3). State 1 Env is likely to represent a non-liganded conformation in pre-triggered trimers that have a closed structure. State 2 represents an intermediate conformation, which is observed for the non-CD4-bound Env protomer in an asymmetric Env trimer where other protomer(s) is bound to CD4. State 3 Env is observed with the Env protomer bound to CD4, which has an open conformation. In non-liganded Env, the V1/V2 loop masks the V3 loop that binds to coreceptors, CCR5 and CXCR4. Once CD4 binds to Env, the V3 loop is exposed. High-resolution structure of State 1 Env has not been determined. Created with BioRender.com.