Insights into the mechanism of dihydropyrimidine dehydrogenase from site-directed mutagenesis targeting the active site loop and redox cofactor coordination

• In mammals, the pyrimidines uracil and thymine are metabolised by a three-step reductive degradation pathway. Dihydropyrimidine dehydrogenase (DPD) catalyses its first and rate-limiting step, reducing uracil and thymine to the corresponding 5,6-dihydropyrimidines in an NADPH-dependent reaction. The enzyme is an adjunct target in cancer therapy since it rapidly breaks down the anti-cancer drug 5-fluorouracil and related compounds. Five residues located in functionally important regions were targeted in mutational studies to investigate their role in the catalytic mechanism of dihydropyrimidine dehydrogenase from pig. Pyrimidine binding to this enzyme is accompanied by active site loop closure that positions a catalytically crucial cysteine (C671) residue. Kinetic characterization of corresponding enzyme mutants revealed that the deprotonation of the loop residue H673 is required for active site closure, while S670 is important for substrate recognition. Investigations on selected residues involved in binding of the redox cofactors revealed that the first FeS cluster, with unusual coordination, cannot be reduced and displays no activity when Q156 is mutated to glutamate, and that R235 is crucial for FAD binding.

Subject headings

NATURVETENSKAP  -- Biologi -- Biokemi och molekylärbiologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Biochemistry and Molecular Biology (hsv//eng)

Keyword

Dihydropyrimidine dehydrogenase

Flavoprotein

Iron-sulfur clusters

Site-directed mutagenesis

Oxidoreductase

Pyrimidine degradation

Biochemistry

Biokemi

Molecular biology

Molekylärbiologi

Publication and Content Type

ref (subject category)

art (subject category)