Paired Bacillus anthracis Dps (mini-ferritin) have different reactivities with peroxide

Abstract

Dps (DNA protection during starvation) proteins, mini-ferritins in the ferritin superfamily, catalyze Fe2+/H2O2/O-2 reactions and make minerals inside protein nanocages to minimize radical oxygen-chemistry (metal/osmotic/temperature/nutrient/oxidant) and sometimes to confer virulence. Paired Dps proteins in Bacillus, rare in other bacteria, have 60% sequence identity. To explore functional differences in paired Bacilli Dps protein, we measured ferroxidase activity and DNA protection (hydroxyl radical) for Dps protein dodecamers from Bacillus anthracis (Ba) since crystal structures and iron mineralization (iron-stain) were known. The self-assembled (200 kDa) Ba Dps1 (Dlp-1) and Ba Dps2 (Dlp-2) proteins had similar Fe2+/O-2 kinetics, with space for minerals of 500 iron atoms/protein, and protected DNA. The reactions with Fe2+ were novel in several ways: 1) Ba Dps2 reactions (Fe2+/H2O2) proceeded via an A(650) nm intermediate, with similar rates to maxi-ferritins (Fe2+/O-2), indicating a new Dps protein reaction pathway, 2) Ba Dps2 reactions (Fe2+/O-2 versus Fe2+/O-2 + H2O2) differed 3-fold contrasting with Escherichia coli Dps reactions, with 100-fold differences, and 3) Ba Dps1, inert in Fe2+/H2O2 catalysis, inhibited protein-independent Fe2+/H2O2 reactions. Sequence similarities between Ba Dps1 and Bacillus subtilis DpsA(Dps1), which is regulated by general stress factor (SigmaB) and Fur, and between Ba Dps2 and B. subtilis MrgA, which is regulated by H2O2 (PerR), suggest the function of Ba Dps1 is iron sequestration and the function of Ba Dps2 is H2O2 destruction, important in host/pathogen interactions. Destruction of H2O2 by Ba Dps2 proceeds via an unknown mechanism with an intermediate similar spectrally (A(650) nm) and kinetically to the maxi-ferritin diferric peroxo complex.