Crystal structure of the productive ternary complex of dihydropyrimidine dehydrogenase with NADPH and 5-iodouracil. Implications for mechanism of inhibition and electron transfer.
Primary Citation of Related Structures: 1GT8, 1GTE, 1GTH
PubMed Abstract:
Dihydroprymidine dehydrogenase catalyzes the first and rate-limiting step in pyrimidine degradation by converting pyrimidines to the corresponding 5,6- dihydro compounds. The three-dimensional structures of a binary complex with the inhibitor 5-iodouracil and two ternary complexes with NADPH and the inhibitors 5-iodouracil and uracil-4-acetic acid were determined by x-ray crystallography ...
Dihydroprymidine dehydrogenase catalyzes the first and rate-limiting step in pyrimidine degradation by converting pyrimidines to the corresponding 5,6- dihydro compounds. The three-dimensional structures of a binary complex with the inhibitor 5-iodouracil and two ternary complexes with NADPH and the inhibitors 5-iodouracil and uracil-4-acetic acid were determined by x-ray crystallography. In the ternary complexes, NADPH is bound in a catalytically competent fashion, with the nicotinamide ring in a position suitable for hydride transfer to FAD. The structures provide a complete picture of the electron transfer chain from NADPH to the substrate, 5-iodouracil, spanning a distance of 56 A and involving FAD, four [Fe-S] clusters, and FMN as cofactors. The crystallographic analysis further reveals that pyrimidine binding triggers a conformational change of a flexible active-site loop in the alpha/beta-barrel domain, resulting in placement of a catalytically crucial cysteine close to the bound substrate. Loop closure requires physiological pH, which is also necessary for correct binding of NADPH. Binding of the voluminous competitive inhibitor uracil-4-acetic acid prevents loop closure due to steric hindrance. The three-dimensional structure of the ternary complex enzyme-NADPH-5-iodouracil supports the proposal that this compound acts as a mechanism-based inhibitor, covalently modifying the active-site residue Cys-671, resulting in S-(hexahydro-2,4-dioxo-5-pyrimidinyl)cysteine.
Related Citations:
Crystallization and Preliminary X-Ray Study of Pig Liver Dihydropyrimidine Dehydrogenase Dobritzsch, D., Persson, K., Schneider, G., Lindqvist, Y. (2001) Acta Crystallogr D Biol Crystallogr 57: 153
Organizational Affiliation:
Division of Molecular Structural Biology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, S-17177 Stockholm, Sweden.
CA [auth D] DA [auth D] E [auth A] EA [auth D] F [auth A]
CA [auth D], DA [auth D], E [auth A], EA [auth D], F [auth A], FA [auth D], G [auth A], H [auth A], M [auth B], N [auth B], O [auth B], P [auth B], U [auth C], V [auth C], W [auth C], X [auth C]
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