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

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Figure 1<br />

Diagram of cAPK fold. (a) Stereo MOLSCRIPT diagram. (b) The key loops<br />

are as follows: phosphate anchor located between strand 1 and strand 2,<br />

catalytic loop located between strands 6 and 7, DFG motif located between<br />

strands 8 and 9, activation loop including P+1 site between strand 9 and<br />

helix F. Phosphorylation site Thr197 is indicated <strong>by</strong> a large circle,<br />

inhibitor PKI (5–24) is colored in dark, and the P site in the peptide<br />

is shown in the dark circle. This figure has been generated using<br />

MOLSCRIPT [27].<br />

Page 215<br />

Following the connectivity diagram, helix A is connected to β-strand 1, then to the phosphate anchor<br />

encompassing signature motif Gly50XGly 52XXGly55. The β-strand 2 is followed <strong>by</strong> β-strand 3<br />

carrying invariant Lys72. Three antiparallel beta strands create the unique fold of the nucleotide binding<br />

site of the protein kinase. The β-strands 3 is followed <strong>by</strong> helix B, which is present only in cAPK, helix<br />

C, and β-strands 4 and 5. Helix C shows the largest displacements among many different protein kinase<br />

structures and consists of invariant Glu91, which forms a salt bridge with Lys72. This salt bridge is<br />

absent in the inactive CDK-2 structure [1] but present in the crystal structure of the complex of CDK-2<br />

and its activator-cyclin [7]. Displacement of helix C is perhaps most pronounced in the case of the<br />

insulin receptor tyrosine kinase structure (IRK) [3]. In PKA, Phe185 resides in the hydrophobic pocket<br />

formed <strong>by</strong> the hydrophobic residues of helix C (upper lobe) and Tyr164 (lower lobe). In the IRK crystal<br />

structure, the hydrophobic residues of helix C, which provide the pocket for invariant Phe185 (of DFG<br />

motif), no longer interact with<br />

http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_215.html [4/5/2004 5:06:47 PM]

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