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netLibrary - eBook Summary Structure-based Drug Design by ...

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Figure 4<br />

<strong>Structure</strong> of PNP as stereo drawings. (A) Crystal packing. The low-resolution<br />

surfaces of six trimers are shown. The top level is related to the bottom level <strong>by</strong> a 2-fold<br />

axis along X. The distance between the 3-fold axes is 143 Å. A drug molecule is shown<br />

in the solvent channel near the entrance to an active site. (B) Ribbon drawing. The<br />

lowermost trimer of Figure 4A is shown. This is the native structure; the guanine and<br />

phosphate are shown to mark the active site. (C) The swinging gate. The trimer of Figure<br />

4B is rotated about 30° counterclockwise in the plane, followed <strong>by</strong> a roughly 90° rotation<br />

about X to view the entrance to the active site. A model of the transition state is shown<br />

as a line drawing. Conformational changes of the protein on binding guanine are shown.<br />

Arrows are drawn from the C α positions in the native structure to their positions in the<br />

complex. (D) Active site of PNP. The orientation is approximately that of Figure 4C, but<br />

enlarged and clipped to focus on the substrate. Key side-chain residues are labeled.<br />

Residue 159'F, in the center of figure toward the viewer, is the only residue from the<br />

adjacent subunit. The guanosine and phosphate are shown with thicker bonds. Oxygen<br />

and sulfur atoms are shown as white spheres, nitrogen and phosphorus as black spheres.<br />

(E) Purine binding pocket. The style is the same as Figure 4D, but the figure is rotated<br />

slightly and enlarged. The key group interacting with bound guanine are highlighted. (F)<br />

The best inhibitor. The style is the same as Figure 4D, but the figure has been enlarged<br />

and rotated to place the phosphate binding site far from the viewer in the upper left.<br />

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