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. 2006 Feb 13;103(8):2576–2581. doi: 10.1073/pnas.0510144103

Fig. 3.

Fig. 3.

Substrate entry channel and gating mechanism in PAI. (a) The surface potential of PAI shows an electropositive area localized at the entrance of the channel that is created by Lys-85, Arg-87, Lys-102, and Lys-195. The PEG 400 molecule marks the entry of the channel. (b) The molecular surface (blue) of part of the PEG 400 molecule bound to PAI in the absence of substrate/product shows the 30-Å path from the surface to the active site FAD (drawn as sticks). (c) Conformational changes in active site associated with PEG 400 binding reveal the gating mechanism. PEG 400, Phe-193, and Arg-88 are in the open conformation when PEG 400 is bound (blue) compared with the apoenzyme (gray). Arg-88 displays two conformations in the open form of PAI, both of which point away from the entering substrate.