Arginine racemization by coupled catabolic and anabolic dehydrogenases.
D-amino acids exist in living organisms as specialized components of many different machineries. Biosynthesis of D-amino acids from racemization of predominant L-enantiomers is catalyzed by a single enzyme. Here, we report the finding of a novel 2-component amino acid racemase for D-to-L inversion in D-arginine metabolism of Pseudomonas aeruginosa. From DNA microarray analysis, the putative dauBAR operon (for D-arginine utilization) of unknown functions was found to be highly induced by D-arginine. The importance of the dau operon in D-arginine metabolism was demonstrated by the findings that strains with a lesion at dauA or dauB failed to use D-arginine as sole carbon source. Two lines of evidence suggest that DauA and DauB are required for D-to-L racemization of arginine. First, growth complementation of an L-arginine auxotroph by D-arginine was abolished by a lesion at dauA or dauB. Second, D-arginine induced L-arginine-specific genes in the parental strain PAO1 but not in its dauA or dauB mutants. This hypothesis was further supported by activity measurements of the purified enzymes: DauA catalyzes oxidative deamination of D-arginine into 2-ketoarginine and ammonia, and DauB is able to use 2-ketoarginine and ammonia as substrates and convert them into L-arginine in the presence of NADPH or NADH. Thus, we propose that DauA and DauB are coupled catabolic and anabolic dehydrogenases to perform D-to-L racemization of arginine, which serves as prerequisite of D-arginine utilization through L-arginine catabolic pathways.
Li
Congran
C
Department of Biology, 24 Peachtree Center Avenue, Georgia State University, Atlanta, GA 30303, USA.
Lu
Chung-Dar
CD
D000217:Acyltransferases / Q000502:physiology; D000594:Amino Acid Oxidoreductases / Q000502:physiology*; D001120:Arginine / Q000737:chemistry / Q000378:metabolism*; D019295:Computational Biology; D020411:Oligonucleotide Array Sequence Analysis; D010641:Phenotype; D011401:Promoter Regions, Genetic; D011550:Pseudomonas aeruginosa / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D013237:Stereoisomerism
D001120:Arginine; D000594:Amino Acid Oxidoreductases; C040983:arginine oxidase; D000217:Acyltransferases; C047082:arginine succinyltransferase