Characterization of a molybdenum cofactor biosynthetic gene cluster in Rhodobacter capsulatus which is specific for the biogenesis of dimethylsulfoxide reductase

The DMSO reductase of Rhodobacter capsulatus contains a pterin molybdenum c ofactor (Moco) and is located in the periplasm. DNA sequence analysis ident ified four genes involved in the biosynthesis of the Moco (moaA, moaD, moeB and moaC) immediately downstream of the dor (DMSO respiratory) gene cluste r. Rhodobacter capsulatus MoaA was expressed in Escherichia coli as a His(6 )-tagged protein. Although, the expressed protein formed inclusion bodies, EPR spectroscopy showed that MoaA contains a [3Fe-4S] cluster. A moaA mutan t was constructed and its phenotype indicates that the Moco biosynthetic ge ne cluster downstream of the dor operon is specific for the biogenesis of D MSO reductase. Two forms of DMSO reductase were purified by immunoaffinity chromatography from the moaA mutant. A mature form of DMSO reductase was lo cated in the periplasm and a precursor form was found in the cytoplasm.