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

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Figure 5<br />

The S 3 specificity pocket of human renin occupied <strong>by</strong> phenylalanine in the<br />

cyclohexylnorstatine inhibitor.<br />

Page 335<br />

helix h 3 bring it closer <strong>by</strong> (<strong>by</strong> ˜0.5Å) to the substrate-binding site than in mouse renin. It is orientated in<br />

such a fashion in human renin that, although it can accommodate the isobutyl side chain of isoleucine at<br />

P 2', aromatic rings on substituents such as phenylalanine and tyrosine will have severe short contacts<br />

with the side chain of Ile130 (valine in mouse renin). Thus the reorientation of a helix, coupled with<br />

subtle differences in the shapes of the side chains, makes significant changes in the substrate specificity<br />

at this subsite. It is interesting to note that in pepsin this helix is in a similar position with respect to the<br />

active site as in human renin. This provides a structural rationale for the negative influence of peptides<br />

containing phenylalanine [48], tyrosine, or histidine [49] at this subsite (S 2') on the rate of proteolytic<br />

pepsin cleavage, while isoleucine and valine enhance catalysis.<br />

Differences in the specificity subsites at S 1' in the human and mouse renins have a more complicated<br />

explanation. At first sight the situation appears to be explained <strong>by</strong> complementarity of the subsites to the<br />

valine and leucine at<br />

http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_335.html (1 of 2) [4/5/2004 5:26:14 PM]

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