Organization of the genes involved in dimethylglycine and sarcosine degradation in Arthrobacter spp.: implications for glycine betaine catabolism.

The nucleotide sequences of two cloned DNA fragments containing the structural genes of heterotetrameric sarcosine oxidase (soxBDAG) and dimethylglycine dehydrogenase (dmg) from Arthrobater spp. 1-IN and Arthrobacter globiformis, respectively, have been determined. Open reading frames were identified in the soxBDAG operon corresponding to the four subunits of heterotetrameric sarcosine oxidase by comparison with the N-terminal amino-acid sequences and the subunit relative molecular masses of the purified enzyme. Alignment of the deduced sarcosine oxidase amino-acid sequence with amino-acid sequences of functionally related proteins indicated that the arthrobacterial enzyme is highly homologous to sarcosine oxidase from Corynebacterium P-1. Deletion and expression analysis, and alignment of the deduced amino-acid sequence of the dmg gene, showed that dmg encodes a novel dimethylglycine oxidase, which is related to eukaryotic dimethylglycine dehydrogenase, and contains nucleotide-binding, flavinylation and folate-binding motifs. The recombinant dimethylglycine oxidase was purified to homogeneity and characterized. The DNA located upstream and downstream of both the soxBDAG and dmg genes is predicted to encode enzymes involved in the tetrahydrofolate-dependent assimilation of methyl groups. Based on the sequence analysis reported herein, pathways are proposed for glycine betaine catabolism in Arthrobacter species, which involve the identified folate-dependent enzymes.