Characterization of DsrD and its interaction with the DsrAB dissimilatory sulfite reductase.

Microbial dissimilatory sulfate reduction is a key process in the global sulfur and carbon cycles in anoxic ecosystems. In this anaerobic respiration, sulfate is phosphorylated and reduced to sulfite, which is further reduced to a DsrC-trisulfide by the dissimilatory sulfite reductase DsrAB. DsrD is a small protein that acts as an allosteric activator of DsrAB, increasing the efficiency of sulfite reduction. Here, we report a detailed study of DsrD and its interaction with DsrAB. Sequence similarity analyses show that there are three groups of DsrD in organisms with a reductive-type DsrAB. The protein regions involved in the DsrD-DsrAB interaction and activity-promoting effect were investigated through in vitro and in silico studies, including mutations of conserved DsrD residues. The results reveal that the conserved β-loop of DsrD is involved in the interaction, contributing to a better understanding of its mechanism of action.