Isolation of oxygen-dependent nicotine- and pseudooxynicotine-metabolizing enzymes
NicA2 is a flavin-bound amine dehydrogenase from Pseudomonas putida S16 that converts nicotine to the pharmacologically inactive N-methylmyosmine. In animal models of nicotine addiction, injection of NicA2 can decrease nicotine-seeking behavior 10-fold. Accordingly, NicA2-related enzymes have been investigated as smoking-cessation therapeutics. However, efficient catalysis by NicA2 in Pseudomonas putida relies on electron transfer to CycN, a cytochrome c, and not directly to O2. Impractically high amounts of NicA2 are thus necessary to achieve a pharmacological effect in the absence of CycN. Directed evolution has improved the ambient-O2 value of kcat from 0.007 s-1 to 1 s-1 for NicA2, but further improvements have been challenging. Here, we identify a strain of Peribacillus frigoritolerans NIC8 which encodes two flavin amine oxidoreductases, Ncox and Pnox. In the presence of oxygen, Ncox and Pnox act on nicotine and pseudooxynicotine respectively with apparent kcat values of 7.7 s-1 and 3.9 s-1. Transient kinetics establishes bimolecular rate constants of 51100 M-1s-1 and 81000 M-1s-1 for the half-reactions between Ncox and O2 and between Pnox and O2 respectively, consistent with Ncox and Pnox being bona-fide oxidases. Transcriptomics shows enhanced expression of Ncox and Pnox under nicotine-dependent growth as well as supporting the identification of downstream enzymes. Phylogenetic analysis suggests that Ncox and Pnox arose out of repurposing of homologous enzymes found in Bacillus species. The enzymes we describe may be useful for the development of nicotine addiction therapeutics and for bioconversion of nicotine in waste streams.