Pseudomonas aeruginosa Dps (PA0962) Functions in H₂O₂ Mediated Oxidative Stress Defense and Exhibits In Vitro DNA Cleaving Activity

We report the structural, biochemical, and functional characterization of the product of gene PA0962 from Pseudomonas aeruginosa PAO1. The protein, termed Pa Dps, adopts the Dps subunit fold and oligomerizes into a nearly spherical 12-mer quaternary structure at pH 6.0 or in the presence of divalent cations at neutral pH and above. The 12-Mer Pa Dps contains two di-iron centers at the interface of each subunit dimer, coordinated by conserved His, Glu, and Asp residues. In vitro, the di-iron centers catalyze the oxidation of Fe²⁺ utilizing H₂O₂ (not O₂) as an oxidant, suggesting Pa Dps functions to aid P. aeruginosa to survive H₂O₂-mediated oxidative stress. In agreement, a P. aeruginosa Δdps mutant is significantly more susceptible to H₂O₂ than the parent strain. The Pa Dps structure harbors a novel network of Tyr residues at the interface of each subunit dimer between the two di-iron centers, which captures radicals generated during Fe²⁺ oxidation at the ferroxidase centers and forms di-tyrosine linkages, thus effectively trapping the radicals within the Dps shell. Surprisingly, incubating Pa Dps and DNA revealed unprecedented DNA cleaving activity that is independent of H₂O₂ or O₂ but requires divalent cations and 12-mer Pa Dps.