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Figure 5<br />

(a) Staurosporine molecule docked in the ATP binding site of PKA.<br />

hydrogen bonds anchoring staurosporine molecule in the active site of PKA<br />

consists of the 6-amino group and N1 nitrogen and carbonyl of Glu121 and<br />

the amide hydrogen atom of Val123. This bidentate hydrogen bond formation<br />

has been observed in all complexes of protein kinases and ATP solved so far.<br />

(b) Inhibitor of CGP 52411 and ATP docked on the active site of PKA.<br />

Residues of Glu127 and Glu170 are also shown and these are not<br />

conserved in the EGFR kinase.<br />

Page 223<br />

(Figure 5a). This key observation is supported <strong>by</strong> chemical data of lactam amide derivatives, which<br />

provide a plausible model of staurosporine inhibition. This is in the protonated boat-type conformation<br />

found to fit in the ATP binding cleft with minimal steric hindrance. In this model, the 4-amino group<br />

forms hydrogen bonds with the backbone carbonyl of Glu170 and the carboxylate group of Glu127 of<br />

cAPK. A model of the EGFR kinase shows that Glu127 and 170 are replaced <strong>by</strong> Cys and Arg,<br />

respectively (Figure 5b). Replacement of Glu127 <strong>by</strong> Cys is critical according to the model and explains<br />

the several-fold decrease of potency of staurosporine inhibitor toward the EGFR kinase (IC 50=630 nM<br />

http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_223.html (1 of 2) [4/5/2004 5:07:30 PM]

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