2-OXO-1,2-DIHYDROQUINOLINE 8-MONOOXYGENASE - PHYLOGENETIC RELATIONSHIP TO OTHER MULTICOMPONENT NONHEME IRON OXYGENASES

2-Oxo-1,2-dihydroquinoline 8-monooxygenase, an enzyme involved in quin oline degradation by Pseudomonas putida 86, had been identified as a c lass IB two-component nonheme iron oxygenase based on its biochemical and biophysical properties (B. Rosche, B. Tshisuaka, S. Fetzner, and F . Lingens, J. Biol. Chem. 270:17836-17832, 1995). The genes oxoR and o xoO, encoding the reductase and the oxygenase components of the enzyme , were sequenced and analyzed. oxoR was localized approximately 15 kb downstream of oxoO. Expression of both genes was detected in a recombi nant Pseudomonas strain. In the deduced amino acid sequence of the NAD H: (acceptor) reductase component (OxoR, 342 amino acids), putative bi nding sites for a chloroplast-type [2Fe-2S] center, for flavin adenine dinucleotide, and for NAD were identified. The arrangement of these c ofactor binding sites is conserved in all known class IB reductases. A dendrogram of reductases confirmed the similarity of OxoR to other cl ass IB reductases. The oxygenase component (OxoO, 446 amino acids) har bors the conserved amino acid motifs proposed to bind the Rieske-type [2Fe-2S] cluster and the mononuclear iron. In contrast to known class IB oxygenase components, which are composed of differing subunits, Oxo O is a homomultimer, which is typical for class IA oxygenases. Sequenc e comparison of oxygenases indeed revealed that OxoO is more related t o class IA than to class IB oxygenases. Thus, 2-oxo-1,2-dihydroquinoli ne 8-monooxygenase consists of a class IB-like reductase and a class Z A-like oxygenase. These results support the hypothesis that multicompo nent enzymes may be composed of modular elements having different phyl ogenetic origins.