English: Figure 1. Functioning as a dimmer of two identical subunits, HIV protease has a crab-like shape. Its catalytic cleft is gated by a pair of flaps (or pincers if viewed as a crab). When the enzyme is in an inhibitor-free state, the pincer-gate is open, allowing substrates to enter the catalytic cleft; when in an inhibitor-binding state, the pincer-gate is closed, blocking the entrance.
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