Unique primary structure of 2-nitropropane dioxygenase from Hansenula mrakii

We have isolated the gene encoding 2-nitropropane dioxygenase from Hansenula mrakii, an FAD enzyme that catalyzes the oxygenative denitrification of various anionic nitroalkanes. The gene contained an open reading frame consisting of 1122 nucleotides corresponding to 374 amino acid residues. The protein molecular mass was estimated to be 41,466 Da, which was similar to the subunit molecular mass of the enzyme determined by SDS/PAGE. Several FAD enzymes such as D-amino acid oxidase and glucose oxidase also catalyze the oxidation of nitroalkanes as a side-reaction, although not so efficiently [Kido, T. & Soda, K. (1984) Arch. Biochem. Biophys. 234, 468-475]. However, we found no proteins in the databases (GenBank, EMBL, PIR and SWISS-PROT) which are homologous to 2-nitropropane dioxygenase of H. mrakii in primary structure. No protein motifs, including a nucleotide-binding motif, GXGXXG, were found in PROSITE, a database of biologically significant protein sites and patterns. Accordingly, 2-nitropropane dioxygenase is a new type of flavoprotein with a unique structure.