High-resolution structures of scytalone dehydratase-inhibitor complexes crystallized at physiological pH

Scytalone dehydratase is a molecular target of inhibitor design efforts aim ed at preventing the fungal disease caused by Magnaporthe grisea. A method for cocrystallization of enzyme with inhibitors at neutral pH has produced several crystal structures of enzyme-inhibitor complexes at resolutions ran ging from 1.5 to 2.2 Angstrom Four high resolution structures of different enzyme-inhibitor complexes are described. In contrast to the original X-ray structure of the enzyme, the four new structures have well-defined electro n density for the loop region comprising residues 115-119 and a different c onformation between residues 154 and 160. The structure of the enzyme compl ex with an aminoquinazoline inhibitor showed that the inhibitor is in a pos ition to form a hydrogen bond with the amide of the Asn131 side chain and w ith two water molecules in a fashion similar to the salicylamide inhibitor in the original structure, thus confirming design principles. The aminoquin azoline structure also allows for a more confident assignment of donors and accepters in the hydrogen bonding network, The structures of the enzyme co mplexes with two dichlorocyclopropane carboxamide inhibitors showed the two chlorine atoms nearly in plane with the amide side chain of Asn131. The po sitions of Phe53 and Phe158 are significantly altered in the new structures in comparison to the two structures obtained from crystals grown at acidic pH, The multiple structures help define the mobility of active site amino acids critical for catalysis and inhibitor binding. Proteins 1999;35:425-43 9. (C) 1999 Wiley-Liss, Inc.