Fig. 1.

The two experimentally determined conformations of HIV-PR. (A) Free HIV-PR with semiopen conformation of flaps (PDB ID code 1HHP). (B) Inhibitor-bound HIV-PR with closed flaps (PDB ID code 1HVR). Importantly, the handedness of the flaps changes in the two forms and is depicted above each structure. Color indicates distinct regions. Flaps: residues 43–58 and 43′-58′, red for free and blue for bound; flap tips: residues 49–52, yellow; flap elbow: residues 37–42, magenta; cantilever: residues 59–75, green; fulcrum: residues 10–23, orange; and interleaved β-strand motif forming the dimer interface: residues 1–4 and 96–99, blue/cyan.