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Brennan et al. BMC Microbiology (2015) 15:99 DOI 10.1186/s12866-015-0430-RESEARCH ARTICLEOpen AccessCloning, expression, and characterization of a Coxiella burnetii Cu/Zn Superoxide dismutaseRobert E Brennan1*, Katalin Kiss2, Rachael Baalman1 and James E SamuelAbstractBackground: Periplasmically localized copper-zinc co-factored superoxide dismutase (SodC) enzymes have been identified in a wide range of Gram-negative bacteria and are proposed to protect bacteria from exogenously produced toxic oxygen radicals, which indicates the potential significance of a Coxiella burnetii SodC. Results: Assays for SOD activity demonstrated that the cloned C. burnetii insert codes for a SOD that was active over a wide range of pH and inhibitable with 5 mM H2O2 and 1 mM sodium diethyldithiocarbamate, a characteristic of Cu/ZnSODs that distinguishes them from Fe or Mn SODs. The sodC was expressed by C. burnetii, has a molecular weight of approximately 18 kDa, which is consistent with the predicted molecular weight, and localized towards the periphery of C. burnetii. Over expression of the C. burnetii sodC in an E. coli sodC mutant restored resistance to H2O2 killing to wild type levels. Conclusions: We have demonstrated that C. burnetii does express a Cu/ZnSOD that is functional at low pH, appears to be excreted, and was able to restore H2O2 resistance in an E. coli sodC mutant. Taken together, these results indicate that the C. burnetii Cu/ZnSOD is a potentially important virulence factor. Keywords: Coxiella, Copper-zinc superoxide dismutase, Q feverBackground Coxiella burnetii, the etiologic agent of Q fever, is an obligate intracellular bacterium that replicates within the phagolysosome of monocytes/macrophages. The ability to survive in the harsh environment of the phagolysosome may require the subversion of macrophage PD98059MedChemExpress PD98059 microbicidal mechanisms. Several enzyme systems potentially required to survive in the phagolysosomal compartment, such as catalase, cytoplasmically localized superoxide dismutase (SOD), and acid phosphatase have been partially characterized [1,2]. Catalase and SOD activities were detected in C. burnetii whole cell lysates and were demonstrated to be maximally active at neutral pH suggesting that these enzymes were cytoplasmically localized and may be involved in detoxifying endogenously generated oxygen radicals [1]. Additionally, Heinzen et al. were able to clone a C. burnetii SOD and functionally complement an E. coli sodA sodB double mutant [2]. This C. burnetii SOD was demonstrated to be homologous to known* Correspondence: [email protected] 1 Department of Biology, University of Central Oklahoma, 100 North University Drive, Edmond, OK, USA Full list of author information is available at the end of the articleiron-containing SODs. Baca et al. also demonstrated that supernatants from high-speed centrifugation of sonicated C. burnetii contained acid phosphatase activity that was optimally active at low pH, localized to the periplasmic space of C. burnetii, and was capable of inhibiting superoxide anion production by stimulated human neutrophils, suggesting that this enzyme may prevent killing of the bacteria during uptake by inhibiting the respiratory burs.
