Organization of the DMSO respiratory operon of Rhodobacter capsulatus and its consequences for homologous expression of DMSOR/TMAOR.

: In this report we describe the organization of the respiratory operon from the non-sulfur photosynthetic bacterium Rhodobacter capsulatus and its consequences for homologous expression of recombinant dimethylsulfoxide/trimethylamine N-oxide reductase (DMSOR/TMAOR). This enzyme is of special interest since molybdopterin dinucleotide is its only cofactor. Overexpression of the dmsA gene and production of active enzyme is not possible in E. coli because this bacterium is unable to supply the required complex molybdopterin cofactor. To investigate the catalytic mechanism and binding of the cofactor by structure-based site-directed mutagenesis, and to ensure sufficient production and incorporation of the complex cofactor, we designed a system for homologous expression in R. capsulatus.