2q37

Crystal structure of OHCU decarboxylase in the presence of (S)-allantoin

spinqualitylabelsall models 2q37, resolution 2.50Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D Structural highlights 2q37 is a 1 chain structure with sequence from Arabidopsis thaliana. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance. Method: X-ray diffraction, Resolution 2.5Å Ligands: 3AL, MSE Resources: FirstGlance, OCA, PDBe, RCSB, PDBsum, ProSAT Function TTHL_ARATH Involved in the last two steps of the degradation of uric acid, i.e. the hydrolysis of 5-hydroxyisourate (HIU) to 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline (OHCU) and its stereoselective decarboxylation to (S)-allantoin. Might function as a negative regulator to modulate brassinosteroid-mediated plant growth. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMed The ureide pathway, which mediates the oxidative degradation of uric acid to (S)-allantoin, represents the late stage of purine catabolism in most organisms. The details of uric acid metabolism remained elusive until the complete pathway involving three enzymes was recently identified and characterized. However, the molecular details of the exclusive production of one enantiomer of allantoin in this pathway are still undefined. Here we report the crystal structure of 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline (OHCU) decarboxylase, which catalyzes the last reaction of the pathway, in a complex with the product, (S)-allantoin, at 2.5-A resolution. The homodimeric helical protein represents a novel structural motif and reveals that the active site in each monomer contains no cofactors, distinguishing this enzyme mechanistically from other cofactor-dependent decarboxylases. On the basis of structural analysis, along with site-directed mutagenesis, a mechanism for the enzyme is proposed in which a decarboxylation reaction occurs directly, and the invariant histidine residue in the OHCU decarboxylase family plays an essential role in producing (S)-allantoin through a proton transfer from the hydroxyl group at C4 to C5 at the re-face of OHCU. These results provide molecular details that address a longstanding question of how living organisms selectively produce (S)-allantoin. Structural and functional basis for (S)-allantoin formation in the ureide pathway.,Kim K, Park J, Rhee S J Biol Chem. 2007 Aug 10;282(32):23457-64. Epub 2007 Jun 13. PMID:17567580 From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.

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