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

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Figure 2<br />

The diagrams of the Cα trace of the five kinases, cAPK, CDK2, CDK2-CYCLIN,<br />

IR, MAP. The thin line represents crystallographically determined homologous<br />

regions of the five kinases (R. Karlsson and J.M. Sowadski, personal<br />

communication).<br />

Page 217<br />

crystals of bovine heart mammalian cAPK [15,16]. A comparison between the two structures has shown<br />

that there is rotation of the upper lobe <strong>by</strong> 15 degrees and a translation of 1.9 Å in the mammalian<br />

structure, which results in the opening of the nucleotide binding cleft.<br />

The motion of this lobe, which includes His87, one of the ligands to Thr197 [15], indicates that the<br />

phosphorylation of this site will be important for conformational diversity of the upper lobe. This is<br />

confirmed <strong>by</strong> the varying degrees of displacement of the upper lobe of all structures of the inactive<br />

unphosphorylated protein kinases (see review [17]). The lower lobe of the enzyme starts with helix D,<br />

which is followed <strong>by</strong> helix E and β-strands 6 and 7. The catalytic loop connecting both strands consists<br />

of a critical set of residues with Tyr164 and Arg165 at the beginning of the loop. The Tyr164 residue<br />

forms a hydrogen bond with invariant Asp220. The Arg165 residue, which is present in a great majority<br />

of protein kinases, provides two hydrogen bonds to the oxygens of the phosphate of Thr197. Invariant<br />

Asp166 (the catalytic base) and Asn171 (the ligand to one of the metal sites) are also located within this<br />

loop.<br />

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