Structural homology model of HIV-1_HXB2 gp120 bound to CD4 with human monoclonal antibodies 17b, 2G12, 48d, and VRC03.

(A) Ribbon diagram of HIV-1HXB2 gp120 structural homology model (grey) bound with CD4 domains 1 and 2 (2QAD; yellow) generated by RaptorX with V1 (red), V2 (dark green), V3 (purple), V4 (orange), and V5 (pink) domains and the CD4 binding loop (CD4BL; blue). The image on the right represents the structure on the left rotated 45 degrees to the left. The boxed area of the left structure is magnified in (B) and highlights the residues required for 2G12 epitope recognition which are indicated by light blue spheres (N295, N332, N386, N392, and N448). The upper boxed area of the right structure is magnified in (C) and highlights the binding of the 17b (4RQS; cyan) and 48d (4DVR; gold) Fabs to their respective CD4i epitopes. The lower boxed area of the right structure is magnified in (D) and highlights the interaction of the VRC03 Fab (3SE8; light pink) and the CD4 binding site which contains the CD4BL. The VRC03 Fab also occupies the same space as where the CD4 domains 1 and 2 (yellow) interact with the gp120 subunit.