THE DPSA PROTEIN OF SYNECHOCOCCUS SP STRAIN-PCC7942 IS A DNA-BINDING HEMOPROTEIN - LINKAGE OF THE DPS AND BACTERIOFERRITIN PROTEIN FAMILIES

The Dps family of proteins are a diverse group of bacterial stress-ind ucible polypeptides that bind DNA and likely confer resistance to pero xide damage during periods of oxidative stress and long term nutrient limitation. Some members of the Dps protein family have been shown to form large (similar to 150-kDa), hexameric complexes that bind chromos omal DNA with little sequence specificity. In this paper we report the nucleotide sequence of the dpsA gene from Synechococcus sp. PCC7942 e ncoding a cyanobacterial Dps homolog. The deduced amino acid sequence of the Synechococcus sp. DpsA protein revealed that a carboxyl-termina l domain of the protein was >60% homologous to the COOH-terminal half of bacterioferritin, Other known Dps family members lack such high sim ilarity 60 the bacterioferritins. Purification and spectroscopic analy sis of the Synechococcus sp. DpsA protein complex revealed that the co mplex contains heme and has a weak catalase activity in vitro. Activit y staining of nondenaturing polyacrylamide gels showed that the protei n complex comigrated with both the heme and the catalase activity, and O-2 evolution measurements yielded a maximal specific activity of 1.7 mu mol of H2O2 consumed/mu g of protein(-1) min(-1). We speculate tha t the protein may have a peroxide-consuming mechanism located on the c hromosomal DNA, and we also suggest that this activity may be a necess ary feature to handle the endogenous oxidative stresses associated wit h oxygenic photosynthesis. Last, the evolutionary link between the Dps protein family and the bacterioferritins is discussed.