Identification and characterization of a novel bacterial sulfite oxidase with no heme binding domain from Deinococcus radiodurans

An open reading frame (draSO) encoding a putative sulfite oxidase (SO) was identified in the sequence of chromosome II of Deinococcus radiodurans; the predicted gene product showed significant amino acid sequence homology to several bacterial and eukaryotic SOs, such as the biochemically and structurally characterized enzyme from Arabidopsis thaliana. Cloning of the Deinococcus SO gene was performed by PCR amplification from the bacterial genomic DNA, and heterologous gene expression of a histidine-tagged polypeptide was obtained in a molybdopterin-overproducing strain of Escherichia coli. The recombinant protein was purified to homogeneity by nickel chelating affinity chromatography, and its main kinetic and chemical physical parameters were determined. Northern blot and enzyme activity analyses indicated that draSO gene expression is constitutive in D. radiodurans and that there is no increase upon exposure to thiosulfate and/or molybdenum(II).