Genetic regulation, biochemical properties and physiological importance of arginase from Sinorhizobium meliloti

• Published in: Microbiology (Society for General Microbiology) Vol. 166; no. 5; pp. 484 - 497
• Main Authors: Ide, Alejandra Arteaga, Hernández, Victor M, Medina-Aparicio, Liliana, Carcamo-Noriega, Edson, Girard, Lourdes, Hernández-Lucas, Ismael, Dunn, Michael F
• Format: Journal Article
• Language: English
• Published: England 01.05.2020
• Subjects: Arginase - genetics; Arginase - physiology; Arginine - metabolism; Bacterial Proteins - genetics; Bacterial Proteins - physiology; Gene Expression Regulation; Genetic Complementation Test; Genome, Bacterial; Hydrogen-Ion Concentration; Mutation; Nitrogen - metabolism; Ornithine - metabolism; Recombinant Proteins; Sinorhizobium meliloti - enzymology; Sinorhizobium meliloti - genetics; Sinorhizobium meliloti - physiology; Urea - metabolism; L-ornithine; divalent metal cofactor; Lrp family regulator; L-arginine; arginase
• ISSN: 1350-0872; 1465-2080
• DOI: 10.1099/mic.0.000909

In bacteria, l-arginine is a precursor of various metabolites and can serve as a source of carbon and/or nitrogen. Arginine catabolism by arginase, which hydrolyzes arginine to l-ornithine and urea, is common in nature but has not been studied in symbiotic nitrogen-fixing rhizobia. The genome of the alfalfa microsymbiont 1021 has two genes annotated as arginases, ( ) and ( ). Biochemical assays with purified ArgI1 and ArgI2 (as 6His-Sumo-tagged proteins) showed that only ArgI1 had detectable arginase activity. A 1021 null mutant lacked arginase activity and grew at a drastically reduced rate with arginine as sole nitrogen source. Wild-type growth and arginase activity were restored in the mutant genetically complemented with a genomically integrated gene. In the wild-type, arginase activity and transcription were induced several fold by exogenous arginine. ArgI1 purified as a 6His-Sumo-tagged protein had its highest enzymatic activity at pH 7.5 with Ni as cofactor. The enzyme was also active with Mn and Co , both of which gave the enzyme the highest activities at a more alkaline pH. The 6His-Sumo-ArgI1 comprised three identical subunits based on the migration of the urea-dissociated protein in a native polyacrylamide gel. A Lrp-like regulator ( ) divergently transcribed from was required for arginase induction by arginine or ornithine. This regulator was designated ArgIR. Electrophoretic mobility shift assays showed that purified ArgIR bound to the promoter in a region preceding the predicted transcriptional start. Our results indicate that ArgI1 is the sole arginase in , that it contributes substantially to arginine catabolism and that induction by arginine is dependent on ArgIR.