title: Characterization of a nitroreductase with selective nitroreduction properties in the food and intestinal lactic acid bacterium Lactobacillus plantarum WCFS1.
abstract: Nitroreductases reduce nitroaromatic compounds and other oxidants in living organisms, having interesting implications in environmental and human health. A putative nitrobenzoate reductase encoding gene (lp_0050) was recently annotated in the completed DNA sequence of lactic acid bacterium Lactobacillus plantarum WCFS1 strain. In this research, this L. plantarum gene was cloned and expressed, and the corresponding protein (PnbA) was biochemically characterized. This L. plantarum PnbA reductase is a 216 amino acid residue FMN-flavoprotein, which exhibits 23% identity with Pseudomonas putida and Ralstonia eutropha nitroreductases and <11% identity with those from enterobacteria such as E. cloacae . This reductase also showed 32-43% identity (65-72% similarity) to predicted PnbA proteins from other lactic acid bacteria. It utilized a wide range of electron acceptors including dichlorophenolindophenol (DCPIP), nitroblue tetrazolium (NBT), ferricyanide, and quinones (menadione, benzoquinone), but not pyridinium cations (paraquat and N-methyl-beta-carbolines), and it was inhibited by dicoumarol and diphenyliodonium. HPLC-MS and spectroscopic data showed that it specifically catalyzed the reduction of the 4-nitroaromatic group to the corresponding hydroxylamine in the presence of NAD(P)H. Kinetics parameters (V(max) and K(m)) showed a higher efficiency for the reduction of 2,4-dinitrobenzoate than for the reduction of 4-nitrobenzoate. It was chemoselective for the reduction of 4-nitrobenzoates, being unable to reduce other nitroaromatics. Then, L. plantarum PnbA reductase might be more specific than other microbial nitroreductases that reduce a wider range of nitroaromatic compounds. The physiological and functional role of nitroreductases remain unknown; however, their presence in lactic acid bacteria widely occurring in foods and the human intestinal tract should be of further interest.
authors.affiliation: Instituto de Fermentaciones Industriales, CSIC, Juan de la Cierva 3, 28006 Madrid, Spain.
authors.forename: Hugo
authors.initials: H
authors.lastname: Guillén
authors.forename: Jose Antonio
authors.initials: JA
authors.lastname: Curiel
authors.forename: José María
authors.initials: JM
authors.lastname: Landete
authors.forename: Rosario
authors.initials: R
authors.lastname: Muñoz
authors.forename: Tomás
authors.initials: T
authors.lastname: Herraiz
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D003001:Cloning, Molecular; D005486:Flavin Mononucleotide / Q000737:chemistry / Q000378:metabolism; D005516:Food Microbiology; D006801:Humans; D007422:Intestines / Q000382:microbiology; D007700:Kinetics; D019344:Lactic Acid / Q000378:metabolism*; D048191:Lactiplantibacillus plantarum / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics / Q000302:isolation & purification; D008969:Molecular Sequence Data; D009579:Nitrobenzoates / Q000737:chemistry / Q000378:metabolism; D009601:Nitroreductases / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D010084:Oxidation-Reduction; D016415:Sequence Alignment; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D009579:Nitrobenzoates; D019344:Lactic Acid; C109832:2,4-dinitrobenzoic acid; D005486:Flavin Mononucleotide; D009601:Nitroreductases