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Figure 4.
Figure 4. The Interface with Rac1 Is Extensive and Highly
Complementary to the Switch I, Switch II, and Nucleotide Regions
of the GTPase(A) The extensive surface charge complementarity
between the GAP domain and Rac1 is illustrated with a molecular
surface colored by electrostatic potential such that red is
negative (acidic) and blue is positive (basic). Arrows indicate
regions of charge complementarity between the Rac1 and SptP
surfaces. (B and C) The SptP GAP domain (secondary structure
shown in blue and side chains in cyan) interact with the Switch
I (yellow) and Switch II (red) regulatory elements of Rac1 (with
yellow side chains). Hydrogen bonds are indicated by white
dotted lines, and the atoms of nitrogen and oxygen are show in
blue and red, respectively. Water molecules are shown as large
magenta spheres. A large “W” indicates the nucleophilic
water molecule positioned by Gln-61 of Rac. (D) SptP positions
Gln-61 of Rac1 through molecular contacts and inserts Arg-209
into the active site to stabilize the transition state. Hydrogen
bonds are indicated by white dotted lines or as smaller gray
dotted lines for weak bonds. AlF[3] is shown with the fluorides
colored brown and the aluminum gray. The magnesium ion and water
molecules are shown as large blue or magenta spheres,
respectively. GDP carbon bonds are shown in yellow. A large
“W” indicates the nucleophilic water molecule positioned by
Gln-61 of Rac1. The phosphate binding (P loop) and guanine
binding loops (G loops) of Rac1 are shown in purple. The bonds
proposed to form during the phosphoryl transfer are shown as
solid white lines. (E) The interface between the GAP (blue) and
tyrosine phosphatase (purple) domains of SptP consists of
several direct and water-mediated hydrogen bonds as well as a
small hydrophobic interface.
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