DdaR (PA1196) Regulates Expression of Dimethylarginine Dimethylaminohydrolase for the Metabolism of Methylarginines in Pseudomonas aeruginosa PAO1.

Dimethylarginine dimethylaminohydrolases (DDAHs) catalyze the hydrolysis of methylarginines to yield l-citrulline and methylamines as products. DDAHs and their central roles in methylarginine metabolism have been characterized for eukaryotic cells. While DDAHs are known to exist in some bacteria, including and , the physiological importance and genetic regulation of bacterial DDAHs remain poorly understood. To provide some insight into bacterial methylarginine metabolism, this study focused on identifying the key elements or factors regulating DDAH expression in PAO1. First, results revealed that can utilize , -dimethyl-l-arginine (ADMA) as a sole source of nitrogen but not carbon. Second, expression of the gene was observed to be induced in the presence of methylarginines, including -monomethyl-l-arginine (l-NMMA) and ADMA. Third, induction of the gene was shown to be achieved through a mechanism consisting of the putative enhancer-binding protein PA1196 and the alternative sigma factor RpoN. Both PA1196 and RpoN were essential for the expression of the gene in response to methylarginines. On the basis of the results of this study, PA1196 was given the name DdaR, for imethylarginine imethylminohydrolase egulator. Interestingly, DdaR and its target gene are conserved only among strains, suggesting that this particular species has evolved to utilize methylarginines from its environment. Methylated arginine residues are common constituents of eukaryotic proteins. During proteolysis, methylarginines are released in their free forms and become accessible nutrients for bacteria to utilize as growth substrates. In order to have a clearer and better understanding of this process, we explored methylarginine utilization in the metabolically versatile bacterium PAO1. Our results show that the transcriptional regulator DdaR (PA1196) and the sigma factor RpoN positively regulate expression of dimethylarginine dimethylaminohydrolases (DDAHs) in response to exogenous methylarginines. DDAH is the central enzyme of methylarginine degradation, and its transcriptional regulation by DdaR-RpoN is expected to be conserved among strains.