Fig 4.
HIV-1 Env gp120 and gp41 structures. (A) Ribbon diagram of gp120 core containing α-helices (α1-5), β-strands (1-25), with relative positions of variable loops (V1-V5) and N and C-termini shown. The orientation of gp120 in this diagram places the viral membrane toward the top and the cell membrane toward the bottom. When gp120 is bound to CD4 it forms a “bridging sheet” consisting of four β-strands, which separates the inner and outer domains of gp120 relative to their orientation in the trimeric complex. Image reprinted by permission from Macmillan Publishers Ltd: Nature107, copyright 1998. (B) Ribbon diagram of gp120 core (as in panel A) with N- terminus (red) and gp41 interaction site (blue) shown. The inner domain is shown in red and grey and the outer domain is shown in orange. The bridging sheet, which shares elements from both inner and outer domains, is in grey and orange. (C) Trimeric gp120 (same colors as in panel B) bound to three molecules of CD4 (yellow) and Fab from neutralizing antibody 17b (brown), used to stabilize the gp120 structure, superimposed onto the electron density observed by cryoelectron tomography (light grey). Orientation of this structure rotated 90°, which places the viral membrane in the plane of the page, is also shown on the right. Images (panels B, C) reproduced from Pancera et al.113 with permission. (D) Three-dimensional representation of HIV-1 Env in its CD4-bound conformation. (Left) A trimeric Env spike (blue) anchored in the lipid bilayer of the viral membrane (grey) is shown. The white arrow indicates the predicted location of gp41. (Right) Ribbon diagram of gp120 core (red) superimposed on the density map (blue) with V1/V2 loop (yellow) and V3 loop (green) shown. Reprinted by permission from Macmillan Publishers Ltd: Nature115, copyright 2008.