Fig. 5. Overview of Env receptor-induced conformational changes that lead to coreceptor binding and fusion.

a–e, Summary of Env conformational changes, including Envs in prefusion closed (PDB 6UDJ), one CD4-bound closed (class I CD4–HT1), one CD4-bound open (cryo-ET)¹¹, two CD4-bound partially open (class I CD4–HT2) and three CD4-bound (PDB 5VN3) conformations. The class II CD4–HT1 cryo-EM reconstruction was similar to the partially open Env conformation observed by cryo-ET for one CD4-bound Env¹¹, but coordinates were not modelled owing to heterogeneity. Depictions for each Env conformation include: Env schematics in side (a) and top-down (b) views, diagrams describing β-sheet conformations observed in Env gp120s (c), surface representations of structures for each Env conformation with cartoon representations of V1V2 and V3 loops (d) and gp41 structural features (e). a and b created using BioRender.com.