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Figure 9<br />

Points of intervention for IL-1-<strong>based</strong> immunomodulation.<br />

Page 413<br />

obtained from such studies can be imported into the available 3-dimensional structures. A combination<br />

of such structural insights coupled with the bioassay results provide clues leading to IL-1 functional<br />

information. In a previous structural report on IL-1β, we summarized the SDM results and identified a<br />

plausible receptor-binding epitope of interleukin-1 [42]. As mentioned before, electrostatic and<br />

hydrogen-bonding interactions in the loops between strands allow the polypeptide to adopt a<br />

conformation that enables an unusual concentration of polar and charged groups to be presented at the<br />

open end of the barrel. This cluster of charged residues forms an epitope with which IL-1 might bind to<br />

the receptor. Following our proposal, many groups have supported this hypothesis <strong>by</strong> employing<br />

mutagenesis studies. For a list of mutants and their activity results refer to References 42, 56, 59, and 61.<br />

Ju and coworkers are employing SDM to characterize interleukin-1 [55,56,58,61]. Substitution of Lys<br />

for the Asp145 of IL-β (D145K) greatly reduced agonist activity, while retaining 100% binding to the IL-<br />

1RI [56]. Based on the sequence alignment of IL-1β with IL-1Ra, they selected Lys145 of IL-1Ra for<br />

mutagenesis and converted it to an aspartic acid. This mutant analog (IL-1Ra K145D) maintained<br />

receptor binding and gained partial agonist activity [56]. Following this study, Ju and coworkers selected<br />

five other amino acid residues in IL-1Ra for further analysis because the side chains of these residues<br />

appear to be in close proximity to Lys145 in IL-1Ra [61]. Mutations were made at Val18, Thr108,<br />

Cys116, Cys122, and Tyr147, usually <strong>by</strong> a replacement with the corresponding amino acid of IL-1β at<br />

each position. None of these muta-<br />

http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_413.html [4/5/2004 5:46:20 PM]

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