(A) Sequence alignment and secondary structure of the HIV-1 p24 capsid protein C-terminal domain (CTD). The aligned sequences are in the following order: BMJ4, P3P24, BNL, B89.6, AE90, BRF, B22, BSG, B90, B92, B93, B94, B249 and GNG. The p24 secondary structure diagram is shown on the top. The α-helices are indicated as bricks. The critical 177 residue is boxed in red. (B) Ribbon (left panel) and surface (right panel) representation of the p24 CTD structure in complex with the A10F9 Fab fragment. The p24 CTDs are in blue and cyan; the Fab light chains are in yellow; and the Fab heavy chains are in magenta. The critical Cys177 residues are labeled in red.