The three-dimensional structure of two polymorphs of a ZLFG-CH2-papain covalent complex has been determined by X-ray crystallography. The structures indicate that: (i) the methylene carbon atom of the inhibitor is covalently bound to the Sgamma atom of Cys25 of papain; (ii) the hydrophobic S2 pocket formed by Pro68, Val133, Val157, and Asp158 is occupied by the inhibitor's phenylalanyl P2 side chain; (iii) extensive hydrogen bonding and hydrophobic interactions are responsible for the interaction of the inhibitor with the enzyme. Comparison with similar structures suggests that in covalent complexes preservation of main chain-main chain interactions between the enzyme and the inhibitor may have higher priority than the P-S interactions.
Two polymorphs of a covalent complex between papain and a diazomethylketone inhibitor.,Janowski R, Kozak M, Jankowska E, Grzonka Z, Jaskolski M J Pept Res. 2004 Oct;64(4):141-50. PMID:15357669
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