The structure of 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline decarboxylase provides insights into the mechanism of uric acid degradation.
The complete degradation of uric acid to (S)-allantoin, as recently elucidated, involves three enzymatic reactions. Inactivation by pseudogenization of the genes of the pathway occurred during hominoid evolution, resulting in a high concentration of urate in the blood and susceptibility to gout. Here, we describe the 1.8A resolution crystal structure of the homodimeric 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline decarboxylase, which catalyzes the last step in the urate degradation pathway, for both ligand-free enzyme and enzyme in complex with the substrate analogs (R)-allantoin and guanine. Each monomer comprises ten alpha-helices, grouped into two domains and assembled in a novel fold. The structure and the mutational analysis of the active site have allowed us to identify some residues that are essential for catalysis, among which His-67 and Glu-87 appear to play a particularly significant role. Glu-87 may facilitate the exit of the carboxylate group because of electrostatic repulsion that destabilizes the ground state of the substrate, whereas His-67 is likely to be involved in a protonation step leading to the stereoselective formation of the (S)-allantoin enantiomer as reaction product. The structural and functional characterization of 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline decarboxylase can provide useful information in view of the potential use of this enzyme in the enzymatic therapy of gout.
Cendron
Laura
L
Department of Chemistry, University of Padua, and Instituto di Chimica Biomolecolare-Consiglio Nazionale delle Ricerche, Section of Padua, Via Marzolo 1, 35131 Padua, Italy; Venetian Institute of Molecular Medicine, Via Orus 2, 35127 Padua, Italy.
Berni
Rodolfo
R
Department of Biochemistry and Molecular Biology, University of Parma, Viale delle Scienze 23/A, 43100 Parma, Italy.
Folli
Claudia
C
Department of Biochemistry and Molecular Biology, University of Parma, Viale delle Scienze 23/A, 43100 Parma, Italy.
Ramazzina
Ileana
I
Department of Biochemistry and Molecular Biology, University of Parma, Viale delle Scienze 23/A, 43100 Parma, Italy.
Percudani
Riccardo
R
Department of Biochemistry and Molecular Biology, University of Parma, Viale delle Scienze 23/A, 43100 Parma, Italy. Electronic address: riccardo.percudani@unipr.it.
Zanotti
Giuseppe
G
Department of Chemistry, University of Padua, and Instituto di Chimica Biomolecolare-Consiglio Nazionale delle Ricerche, Section of Padua, Via Marzolo 1, 35131 Padua, Italy; Venetian Institute of Molecular Medicine, Via Orus 2, 35127 Padua, Italy. Electronic address: giuseppe.zanotti@unipd.it.
D000481:Allantoin / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D002262:Carboxy-Lyases / Q000737:chemistry / Q000502:physiology*; D018360:Crystallography, X-Ray; D004252:DNA Mutational Analysis; D018698:Glutamic Acid / Q000737:chemistry; D006147:Guanine / Q000494:pharmacology; D006639:Histidine / Q000737:chemistry; D008024:Ligands; D008956:Models, Chemical; D008969:Molecular Sequence Data; D017510:Protein Folding; D014527:Uric Acid / Q000378:metabolism*; D015027:Zebrafish; D029961:Zebrafish Proteins / Q000737:chemistry* / Q000502:physiology*
D008024:Ligands; D029961:Zebrafish Proteins; D014527:Uric Acid; D000481:Allantoin; D018698:Glutamic Acid; D006639:Histidine; D006147:Guanine; C522184:2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline decarboxylase, zebrafish; D002262:Carboxy-Lyases