The crystal structure of a novel flavin-containing monooxygenase from Methyiophaga sp. Strain SK1.

FAD-dependent monooxygenases are divided into three classes, flavin-containing monooxygenases (FMO), N-hydroxylating monooxygenase (NMO), and Baeyer-Villiger monooxygenase (BVMO). In prokaryotes, no FMO proteins have been characterized unlike other members of NMO or BVFO classes. A gene from Methlophaga sp. Strain SK1, a restricted facultative methylotroph, of which expression on E. coli produced blue dye indigo was cloned. The deduced amino acid sequence of the gene showed similarity to the mammalian FMOs that convert xenobiotics to more hydrophilic metabolites. This is the first member of the FMO family characterized in prokaryotes. A crystal of recombinant FMO containing hexaHis-tag was obtained under the condition of 1.5 M ammonium sulfate and 5% isopropanol, and the crystal belongs to space group C2. We determined the crystal structure of the FMO by single-wavelength anomalous dispersion at 2.4 Å resolution. FMO is composed of two structural domains, small and large domains. Both domains contain a parallel β-sheet flanked by an antiparallel β-sheet and α helices. The small domain is inserted in the parallel β-sheet of the large domain, which includes C-terminal helices. There is a channel between two domains and a cofactor FAD was found on depressed surface of large domain in the channel. It suggests that the channel is the active site of the FMO. [ABSTRACT FROM AUTHOR]