Fig. 24.12 3D Structure of HIV protease in complex with the peptide substrate Arg–Pro–Gly–Asn–Phe–Leu–Gln–Ser–Arg–Pro. The structure with the substrate could be obtained with a catalytically inactive enzyme because both acidic aspartic acids of the catalytic dyad had been mutated to asparagines. The protease exists as a C2-symmetric homodimer. The peptide chains are shown in green and red, respectively.