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Journal of Bacteriology, March 2008, p. 2206-2216, Vol. 190, No. 6
0021-9193/08/$08.00+0     doi:10.1128/JB.01685-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Structural and Functional Characterization of an Organic Hydroperoxide Resistance Protein from Mycoplasma gallisepticum{triangledown}

Cheryl Jenkins,1* Ram Samudrala,2 Steven J. Geary,3 and Steven P. Djordjevic1

Department of Primary Industries, Elizabeth Macarthur Agricultural Institute, Camden, NSW 2570, Australia,1 Computational Biology Group, Department of Microbiology, University of Washington, Seattle, Washington 98195,2 Center of Excellence for Vaccine Research and Department of Pathobiology and Veterinary Science, The University of Connecticut, Storrs, Connecticut 06269-30893

Received 18 October 2007/ Accepted 2 January 2008

As obligate parasites, Mycoplasma species are continuously exposed to oxidative damage due to host-generated peroxides and reactive oxygen species (ROS). In addition, the production of endogenous oxidants is believed to be a primary virulence mechanism of several Mollicute species, indicating that oxidative stress resistance is crucial to survival of these bacteria in the host milieu. Despite the abundance of oxidants at the site of infection, enzymes responsible for the detoxification of ROS have never been characterized in mycoplasmas. Here we characterize a homolog of the ohr (organic hydroperoxide resistance) family from Mycoplasma gallisepticum (encoding MGA1142). Unlike previously characterized ohr genes, the mga1142 gene is not upregulated in response to oxidative stress but displays a novel pattern of expression. Both organic and inorganic peroxides can act as substrates for MGA1142, but they are degraded with various efficiencies. Furthermore, cumene hydroperoxide, an aromatic peroxide metabolized with high efficiency by other Ohr proteins, was shown to rapidly inactivate MGA1142, accounting for the sensitivity of M. gallisepticum cells to this compound. Comparative modeling of the MGA1142 quaternary structure revealed that the active site of this molecule has a relatively wide conformation. These data indicate that the natural substrate for MGA1142 differs from that for previously characterized Ohr proteins. Triton X-114 partitioning demonstrated that MGA1142 is located in both cytosol and membrane fractions, suggesting that in vivo this molecule plays a role in the detoxification of both endogenous and exogenous peroxides. A model describing how MGA1142 is likely to be oriented in the cell membrane is presented.

* Corresponding author. Mailing address: Microbiology and Immunology, PMB 8, Camden, NSW 2570, Australia. Phone: 61 2 4640 6426. Fax: 61 2 4640 6438. E-mail: cheryl.jenkins{at}dpi.nsw.gov.au

{triangledown} Published ahead of print on 11 January 2008.

Journal of Bacteriology, March 2008, p. 2206-2216, Vol. 190, No. 6
0021-9193/08/$08.00+0     doi:10.1128/JB.01685-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



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