title: Gene cluster on pAO1 of Arthrobacter nicotinovorans involved in degradation of the plant alkaloid nicotine: cloning, purification, and characterization of 2,6-dihydroxypyridine 3-hydroxylase.
abstract: A 27,690-bp gene cluster involved in the degradation of the plant alkaloid nicotine was characterized from the plasmid pAO1 of Arthrobacter nicotinovorans. The genes of the heterotrimeric, molybdopterin cofactor (MoCo)-, flavin adenine dinucleotide (FAD)-, and [Fe-S] cluster-dependent 6-hydroxypseudooxynicotine (ketone) dehydrogenase (KDH) were identified within this cluster. The gene of the large MoCo subunit of KDH was located 4,266 bp from the FAD and [Fe-S] cluster subunit genes. Deduced functions of proteins encoded by open reading frames (ORFs) of the cluster were correlated to individual steps in nicotine degradation. The gene for 2,6-dihydroxypyridine 3-hydroxylase was cloned and expressed in Escherichia coli. The purified homodimeric enzyme of 90 kDa contained 2 mol of tightly bound FAD per mol of dimer. Enzyme activity was strictly NADH-dependent and specific for 2,6-dihydroxypyridine. 2,3-Dihydroxypyridine and 2,6-dimethoxypyridine acted as irreversible inhibitors. Additional ORFs were shown to encode hypothetical proteins presumably required for holoenzyme assembly, interaction with the cell membrane, and transcriptional regulation, including a MobA homologue predicted to be specific for the synthesis of the molybdopterin cytidine dinucleotide cofactor.
authors.affiliation: Institute of Biochemistry and Molecular Biology, University of Freiburg, Freiburg, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Baitsch
authors.forename: C
authors.initials: C
authors.lastname: Sandu
authors.forename: R
authors.initials: R
authors.lastname: Brandsch
authors.forename: G L
authors.initials: GL
authors.lastname: Igloi
mesh_terms: D000595:Amino Acid Sequence; D001173:Arthrobacter / Q000201:enzymology* / Q000235:genetics; D001673:Biodegradation, Environmental; D003001:Cloning, Molecular; D005798:Genes, Bacterial; D006899:Mixed Function Oxygenases / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D008969:Molecular Sequence Data; D005810:Multigene Family; D009538:Nicotine / Q000378:metabolism*; D016366:Open Reading Frames; D010957:Plasmids / Q000235:genetics*; D011725:Pyridines / Q000378:metabolism
chemical_list: D011725:Pyridines; C014047:hydroxypyridines; D009538:Nicotine; D006899:Mixed Function Oxygenases; C435512:2,6-dihydroxypyridine 3-hydroxylase