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 structu ral genes of heterotetrameric sarcosine oxidase (soxBDAG) and dimethylglyci ne dehydrogenase (dmg) from Arthrobater spp. 1-IN and Arthrobacter globifor mis, respectively, have been determined. Open reading frames were identifie d in the soxBDAG operon corresponding to the four subunits of heterotetrame ric sarcosine oxidase by comparison with the N-terminal amino-acid sequence s and the subunit relative molecular masses of the purified enzyme. Alignme nt of the deduced sarcosine oxidase amino-acid sequence with amino-acid seq uences 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 s equence of the dmg gene, showed that dmg encodes a novel dimethylglycine ox idase, which is related to eukaryotic dimethylglycine dehydrogenase, and co ntains nucleotide-binding, flavinylation and folate-binding motifs. The rec ombinant dimethylglycine oxidase was purified to homogeneity and characteri zed. The DNA located upstream and downstream of both the soxBDAG and dmg ge nes is predicted to encode enzymes involved in the tetrahydrofolate-depende nt assimilation of methyl groups. Based on the sequence analysis reported h erein, pathways are proposed for glycine betaine catabolism in Arthrobacter species, which involve the identified folate-dependent enzymes.