Structure, Functional Characterization, and Evolution of the Dihydroorotase Domain of Human CAD

• Published in: Structure (London) Vol. 22; no. 2; pp. 185 - 198
• Main Authors: Grande-García, Araceli, Lallous, Nada, Díaz-Tejada, Celsa, Ramón-Maiques, Santiago
• Format: Journal Article
• Language: English
• Published: United States Elsevier Ltd 04-02-2014
• Subjects: Amino Acid Sequence; Aspartate Carbamoyltransferase - chemistry; Bacterial Proteins - metabolism; Carbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing) - chemistry; Catalysis; Catalytic Domain; Cell Line; Dihydroorotase - chemistry; DNA Repair; Escherichia coli - enzymology; HEK293 Cells; Histidine - chemistry; Humans; Hydrogen-Ion Concentration; Ions; Lysine - chemistry; Molecular Sequence Data; Mutagenesis, Site-Directed; Neoplasms - metabolism; Phosphorylation; Phylogeny; Protein Binding; Protein Multimerization; Sequence Homology, Amino Acid; Zinc - chemistry
• ISSN: 0969-2126; 1878-4186
• DOI: 10.1016/j.str.2013.10.016

Upregulation of CAD, the multifunctional protein that initiates and controls the de novo biosynthesis of pyrimidines in animals, is essential for cell proliferation. Deciphering the architecture and functioning of CAD is of interest for its potential usage as an antitumoral target. However, there is no detailed structural information about CAD other than that it self-assembles into hexamers of ∼1.5 MDa. Here we report the crystal structure and functional characterization of the dihydroorotase domain of human CAD. Contradicting all assumptions, the structure reveals an active site enclosed by a flexible loop with two Zn2+ ions bridged by a carboxylated lysine and a third Zn coordinating a rare histidinate ion. Site-directed mutagenesis and functional assays prove the involvement of the Zn and flexible loop in catalysis. Comparison with homologous bacterial enzymes supports a reclassification of the DHOase family and provides strong evidence against current models of the architecture of CAD.
•Crystallography reveals the structure of the dihydroorotase domain of human CAD•The catalytic mechanism is based on two Zn ions coordinated by a carboxylated lysine•A third Zn, a rare histidinate ion, and a flexible loop fine-tune the enzyme reaction•Differences with bacterial dihydroorotases discard current models of CAD architecture
Activation of CAD, the multifunctional protein that controls the synthesis of pyrimidines, is essential for cell proliferation. Grande-García et al. determine the structure of the dihydroorotase domain of human CAD, revealing its inner workings and the evolutionary relationship with bacterial enzymes.