FIG 1.

HIV Env trimers can adopt several conformational states. Env gp120 subunits are light gray, gp41 is dark gray, V1V2 regions are orange, and V3 is blue. HIV-1 Envs in different conformational states are shown in side (top) or top (bottom) views. (Left) Closed, prefusion Env trimer conformation with gp120 V1V2 at the apex of the trimer (PDB code 5CEZ); (middle) occluded open conformation with outwardly rotated gp120 protomers but no local structural rearrangements in V1V2 or V3 (PDB code 7TFN); (right) CD4-bound fully open conformation (sCD4 not shown) with V1V2 regions largely disordered and displaced from the trimer apex to the sides of the trimer and the V3 base fully exposed with the remainder of V3 disordered (PDB code 6U0L). Regions that were buried in a closed Env conformation (left) but exposed in the sCD4-bound open conformation (right) are indicated by green shading inside a dotted black oval.