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. Author manuscript; available in PMC: 2013 May 1.
Published in final edited form as: J Struct Biol. 2012 Jan 10;178(2):165–176. doi: 10.1016/j.jsb.2012.01.004

FIGURE 1.

FIGURE 1

Illustration of quaternary conformational states of trimeric Env. Cryo-electron tomographic studies of intact virions and soluble trimeric gp140 have identified distinct arrangements of Env with unliganded gp120 or when it is bound to antibodies or ligands such as sCD4. Schematic representations of four well-defined structures are shown, representing native trimeric Env in the closed conformation, which is observed on CD4-dependent viruses (a), trimeric Env in the open conformation, which is observed on CD4-independent viruses (b), trimeric Env in the open conformation, complexed with sCD4 (c) and trimeric Env in the open conformation complexed with sCD4 and a co-receptor binding site antibody such as 17b or 7D3 (d).