Without inhibitor


With inhibitor

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The X-ray structure of HIV protease (a) uncomplexed; and (b) in complex with the transition state analog inhibitor saquinavir. The homodimeric protein is shown in ribbon form with one subunit gold and the other cyan. The side chains of the active site Asp residues, Asp 25 and Asp 25', as well as the saquinavir in Part b, are shown in ball-and-stick form with C green, N blue, and O red. Highlight the 'β hairpin flaps' to see the position of the flaps (Met46-Lys55) in (a) uncomplexed and (b) in complex with its inhibitor. Note how the beta hairpin "flaps" that are open at the top of the uncomplexed enzyme fold down over the inhibitor in the saquinavir complex. [X-ray structures by Tom Blundell, Birkbeck College, London, U.K., and Robert Crowther, Hoffmann-LaRoche Ltd., Nutley, New Jersey. PDBids 3PHV and 1HXB.]