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Figure 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.
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