5vep
From Proteopedia
MOUSE KYNURENINE AMINOTRANSFERASE III, RE-REFINEMENT OF THE PDB STRUCTURE 3E2F
Structural highlights
Function[KAT3_MOUSE] Catalyzes the irreversible transamination of the L-tryptophan metabolite L-kynurenine to form kynurenic acid (KA). May catalyze the beta-elimination of S-conjugates and Se-conjugates of L-(seleno)cysteine, resulting in the cleavage of the C-S or C-Se bond (By similarity). Has transaminase activity towards L-kynurenine, tryptophan, phenylalanine, serine, cysteine, methionine, histidine, glutamine and asparagine with glyoxylate as an amino group acceptor (in vitro). Has lower activity with 2-oxoglutarate as amino group acceptor (in vitro).[1] Publication Abstract from PubMedKynurenine aminotransferase III (KAT III) has been considered to be involved in the production of mammalian brain kynurenic acid (KYNA), which plays an important role in protecting neurons from overstimulation by excitatory neurotransmitters. The enzyme was identified based on its high sequence identity with mammalian KAT I, but its activity toward kynurenine and its structural characteristics have not been established. In this study, the biochemical and structural properties of mouse KAT III (mKAT III) were determined. Specifically, mKAT III cDNA was amplified from a mouse brain cDNA library, and its recombinant protein was expressed in an insect cell protein expression system. We established that mKAT III is able to efficiently catalyze the transamination of kynurenine to KYNA and has optimum activity at relatively basic conditions of around pH 9.0 and at relatively high temperatures of 50 to 60 degrees C. In addition, mKAT III is active toward a number of other amino acids. Its activity toward kynurenine is significantly decreased in the presence of methionine, histidine, glutamine, leucine, cysteine, and 3-hydroxykynurenine. Through macromolecular crystallography, we determined the mKAT III crystal structure and its structures in complex with kynurenine and glutamine. Structural analysis revealed the overall architecture of mKAT III and its cofactor binding site and active center residues. This is the first report concerning the biochemical characteristics and crystal structures of KAT III enzymes and provides a basis toward understanding the overall physiological role of mammalian KAT III in vivo and insight into regulating the levels of endogenous KYNA through modulation of the enzyme in the mouse brain. Biochemical and structural properties of mouse kynurenine aminotransferase III.,Han Q, Robinson H, Cai T, Tagle DA, Li J Mol Cell Biol. 2009 Feb;29(3):784-93. Epub 2008 Nov 24. PMID:19029248[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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