Gene disruption analysis of DppA isolated as a periplasmic molecular chaperone-like protein for folding of dimethyl sulfoxide reductase in Rhodobacter sphaeroides f. sp. denitrificans.

The effect of inactivation of DppA, a dipeptide transport protein identified as a periplasmic molecular chaperone-like protein, on the formation of active dimethyl sulfoxide reductase (DMSOR) was examined in Rhodobacter sphaeroides f. sp. denitrificans. All of the dppA-disrupted mutants produced a normal level of native form of DMSOR and grew by DMSO respiration, indicating that the loss of DppA protein alone had no effect on the formation of active DMSOR. The periplasmic fraction of the dppA-disrupted mutant also had the activity to prevent aggregation of acid-unfolded DMSOR. Two proteins, DctP and BztA, were further identified as the proteins with the activity. Their activities, however, were much lower than that of DppA. These results suggest that several substrate binding proteins might be implicated in the folding of unfolded DMSOR in the periplasm.