title: Deciphering the genetic determinants for aerobic nicotinic acid degradation: the nic cluster from Pseudomonas putida KT2440.
abstract: The aerobic catabolism of nicotinic acid (NA) is considered a model system for degradation of N-heterocyclic aromatic compounds, some of which are major environmental pollutants; however, the complete set of genes as well as the structural-functional relationships of most of the enzymes involved in this process are still unknown. We have characterized a gene cluster (nic genes) from Pseudomonas putida KT2440 responsible for the aerobic NA degradation in this bacterium and when expressed in heterologous hosts. The biochemistry of the NA degradation through the formation of 2,5-dihydroxypyridine and maleamic acid has been revisited, and some gene products become the prototype of new types of enzymes with unprecedented molecular architectures. Thus, the initial hydroxylation of NA is catalyzed by a two-component hydroxylase (NicAB) that constitutes the first member of the xanthine dehydrogenase family whose electron transport chain to molecular oxygen includes a cytochrome c domain. The Fe(2+)-dependent dioxygenase (NicX) converts 2,5-dihydroxypyridine into N-formylmaleamic acid, and it becomes the founding member of a new family of extradiol ring-cleavage dioxygenases. Further conversion of N-formylmaleamic acid to formic and maleamic acid is catalyzed by the NicD protein, the only deformylase described so far whose catalytic triad is similar to that of some members of the alpha/beta-hydrolase fold superfamily. This work allows exploration of the existence of orthologous gene clusters in saprophytic bacteria and some pathogens, where they might stimulate studies on their role in virulence, and it provides a framework to develop new biotechnological processes for detoxification/biotransformation of N-heterocyclic aromatic compounds.
authors.affiliation: Departments of Molecular Microbiology and Protein Science, Centro de Investigaciones Biológicas-Consejo Superior de Investigaciones Científicas, 28040 Madrid, Spain.
authors.forename: José I
authors.initials: JI
authors.lastname: Jiménez
authors.forename: Angeles
authors.initials: A
authors.lastname: Canales
authors.forename: Jesús
authors.initials: J
authors.lastname: Jiménez-Barbero
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Ginalski
authors.forename: Leszek
authors.initials: L
authors.lastname: Rychlewski
authors.forename: José L
authors.initials: JL
authors.lastname: García
authors.forename: Eduardo
authors.initials: E
authors.lastname: Díaz
mesh_terms: D000332:Aerobiosis / Q000502:physiology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001673:Biodegradation, Environmental; D004579:Electron Transport / Q000502:physiology; D004785:Environmental Pollutants / Q000378:metabolism*; D005798:Genes, Bacterial / Q000502:physiology*; D006900:Hydroxylation; D008298:Maleates / Q000378:metabolism; D005810:Multigene Family / Q000502:physiology*; D009525:Niacin / Q000378:metabolism*; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000502:physiology; D016958:Pseudomonas putida / Q000201:enzymology* / Q000235:genetics; D011725:Pyridines / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004785:Environmental Pollutants; D008298:Maleates; D011725:Pyridines; D009525:Niacin; D010088:Oxidoreductases; C008311:maleamic acid; D010100:Oxygen; C065452:2,5-dihydroxypyridine