TAILIEUCHUNG - Báo cáo Y học: Role of tyrosine 238 in the active site of Rhodotorula gracilis D-amino acid oxidase A site-directed mutagenesis study

Y238, oneof thevery fewconservedresidues in theactive site ofD-amino acid oxidases (DAAO), was mutated to phe-nylalanine and serine in the enzyme from the yeastRhodo-torula gracilis. The mutated proteins are catalytically competent thus eliminating Tyr238 as an active-site acid/ base catalyst. Y238FandY238Smutants exhibit a threefold slower turnover on D-alanine as substrate, which can be attributed to a slower rate of product release relative to the wild-type enzyme (a change of the rate constants for sub-strate binding was also evident). . | Eur. J. Biochem. 269 4762-4771 2002 FEBS 2002 doi Role of tyrosine 238 in the active site of Rhodotorula gracilis D-amino acid oxidase A site-directed mutagenesis study Angelo Boselli Silvia Sacchi Viviana Job Mirella S. Pilone and Loredano Pollegioni Department of Structural and Functional Biology University of Insubria Varese Italy Y238 one of the very few conserved residues in the active site of D-amino acid oxidases DAAO was mutated to phenylalanine and serine in the enzyme from the yeast Rhodo-torula gracilis. The mutated proteins are catalytically competent thus eliminating Tyr238 as an active-site acid base catalyst. Y238F and Y238S mutants exhibit a threefold slower turnover on D-alanine as substrate which can be attributed to a slower rate of product release relative to the wild-type enzyme a change of the rate constants for substrate binding was also evident . The Y238 DAAO mutants have spectral properties similar to those of the wild-type enzyme but the degree of stabilization of the flavin semiquinone and the redox properties in the free form of Y238S are different. The binding of the carboxylic acid competitive inhibitors and the substrate D-alanine are changed only slightly suggesting that the overall substrate binding pocket remains intact. In agreement with data from the pH dependence of ligand binding and with the protein crystal structure site-directed mutagenesis results emphasize the importance of residue Y238 in controlling access to the active site instead of a role in the substrate ligand interaction. Keywords active site lid function-structure relationships flavoprotein reaction mechanism substrate recognition. D-amino acid oxidase DAAO EC an FADcontaining flavoprotein catalyses dehydrogenation of the D-isomer of amino acids to give the corresponding a-imino acids and after subsequent hydrolysis a-keto acids and ammonia. The reduced FAD is then reoxidized by molecular oxygen to yield hydrogen .

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