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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. [ABSTRACT FROM AUTHOR]

The type VI secretion system (T6SS), a protein translocation nanomachine, is widely distributed in Gram-negative bacteria and delivers effectors directly into target cells or the extracellular environment to help the bacteria gain a competitive fitness advantage and promote bacterial survival in harmful environments. In this study, we demonstrated that the synthesis of the Pseudomonas quinolone signal (PQS) in Pseudomonas aeruginosa PAO1 was inhibited by the H3-T6SS gene cluster under iron-rich conditions, and that this inhibition was relieved under iron starvation conditions. Conversely, PQS differentially regulated the expression of the H3-T6SS structural genes and the effector protein gene tseF. The expression of tseF was inhibited by PQS, while the expressions of the H3-T6SS structural genes were positively regulated by PQS. Further studies showed that the H3-T6SS was involved in the resistance of P. aeruginosa to oxidative stress caused by hydrogen peroxide (H2O2). Interestingly, H3-T6SS expression was neither induced by H2O2 stress nor regulated by OxyR (a global anti-oxidative transcriptional regulator) but was positively regulated by RpoS (a major transcription regulator of the stress response). In addition, we found that the clpV3 (a structural gene of H3-T6SS) mutation resulted in upregulation of two proteins related to PQS synthesis and many proteins related to oxidative stress resistance, while the expression of some iron storage proteins, especially Dps, were significantly downregulated. Furthermore, the clpV3 mutation led to an increase in the intracellular free Fe2+ content of P. aeruginosa. Further studies showed that both the PQS deficient mutation and overexpression of dps effectively restored the H2O2 sensitive phenotype of the H3-T6SS mutant. Finally, we proposed the following model of H3-T6SS-mediated resistance to H2O2 stress in P. aeruginosa. H3-T6SS not only reduces the intracellular free Fe2+ level by upregulating the expression of ferritin Dps, but also inhibits the synthesis of PQS to mediate the resistance of P. aeruginosa to H2O2 stress. This study highlights the important role of H3-T6SS in the ability of P. aeruginosa to combat H2O2 stress and provides a perspective for understanding the stress response mechanism of bacteria. [ABSTRACT FROM AUTHOR]

A growing body of research suggests that inflammatory insult contributes to the etiology of central nervous system diseases, such as depression, Alzheimer's disease, and so forth. However, the effect of prenatal systemic inflammation exposure on offspring brain development and cerebral susceptibility to inflammatory insult remains unknown. In this study, we utilized the prenatal inflammatory insult model in vivo and the neuronal damage model in vitro. The results obtained show that prenatal maternal inflammation exacerbates LPS-induced memory impairment, neuronal necrosis, brain inflammatory response, and significantly increases protein expressions of COX-2, DP2, APP, and Aβ, while obviously decreasing that of DP1 and the exploratory behaviors of offspring rats. Meloxicam significantly inhibited memory impairment, neuronal necrosis, oxidative stress, and inflammatory response, and down-regulated the expressions of APP, Aβ, COX-2, and DP2, whereas significantly increased exploring behaviors and the expression of DP1 in vivo. Collectively, these findings suggested that maternal inflammation could cause offspring suffering from inflammatory and behavioral disorders and increase the susceptibility of offspring to cerebral pathological factors, accompanied by COX-2/PGD-2/DPs pathway activation, which could be ameliorated significantly by COX-2 inhibitor meloxicam treatment. [ABSTRACT FROM AUTHOR]