The NprA nitroreductase required for 2,4-dinitrophenol reduction in Rhodobacter capsulatus is a dihydropteridine reductase.
The Rhodobacter capsulatus nprA gene codes for a putative nitroreductase. A recombinant His(6)-NprA protein was overproduced in Escherichia coli and purified by affinity chromatography. This protein contained FMN and showed nitroreductase activity with a wide range of nitroaromatic compounds, such as 2-nitrophenol, 2,4-dinitrophenol, 2,6-dinitrophenol, 2,4,6-trinitrophenol (picric acid), 2,4-dinitrobenzoate and 2,4-dinitrotoluene, and with the nitrofuran derivatives nitrofurazone and furazolidone. NADPH was the main electron donor and the ortho nitro group was preferably reduced to the corresponding amino derivative. The apparent K(m) values of NprA for NADPH, 2,4-dinitrophenol, picric acid and furazolidone were 40 microM, 78 microM, 72 microM and 83 microM, respectively, at pH and temperature optima (pH 6.5, 30 degrees C). Escherichia coli cells overproducing the NprA protein were much more sensitive to the prodrug 5-(aziridin-1-yl)-2,4-dinitrobenzamide (CB1954) used in cancer therapy than non-transformed cells. NprA showed the highest activity with the quinonoid form of 6,7-dimethyl-7,8-dihydropterine as substrate, so that NprA may be involved in the synthesis of tetrahydrobiopterin in R. capsulatus. Expression of a transcriptional nprA-lacZ gene fusion was induced by phenylalanine or tyrosine, but not by other amino acids like glutamate or alanine. Furthermore, both nitroreductase activity and phenylalanine assimilation were inhibited in vivo by ammonium. A mutant defective in the nprA gene showed better growth rate with Phe or Tyr as nitrogen source than the wild-type strain, although both strains showed similar growth in media with Glu or without added nitrogen. These results suggest that the NprA nitroreductase may act in vivo as a dihydropteridine reductase involved in aromatic amino acids metabolism.
Pérez-Reinado
Eva
E
Departamento de Bioquímica y Biología Molecular, Edificio Severo Ochoa, Universidad de Córdoba, Córdoba, Spain.
Roldán
María Dolores
MD
Castillo
Francisco
F
Moreno-Vivián
Conrado
C
D019297:2,4-Dinitrophenol / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D003001:Cloning, Molecular; D003067:Coenzymes / Q000032:analysis; D004093:Dihydropteridine Reductase / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D005486:Flavin Mononucleotide / Q000032:analysis; D017353:Gene Deletion; D015870:Gene Expression; D015964:Gene Expression Regulation, Bacterial; D015971:Gene Expression Regulation, Enzymologic; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009249:NADP / Q000378:metabolism; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification; D016354:Rhodobacter capsulatus / Q000201:enzymology* / Q000235:genetics; D013379:Substrate Specificity; D013696:Temperature
D001426:Bacterial Proteins; D003067:Coenzymes; D011994:Recombinant Proteins; D009249:NADP; D005486:Flavin Mononucleotide; D004093:Dihydropteridine Reductase; D019297:2,4-Dinitrophenol