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Journal of Bacteriology, August 2006, p. 5839-5850, Vol. 188, No. 16
0021-9193/06/$08.00+0     doi:10.1128/JB.00430-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Methionine Sulfoxide Reductase in Helicobacter pylori: Interaction with Methionine-Rich Proteins and Stress-Induced Expression

Praveen Alamuri and Robert J. Maier*

Department of Microbiology, The University of Georgia, Athens, Georgia 30602

Received 28 March 2006/ Accepted 26 May 2006

The reductive repair of oxidized methionine residues performed by methionine sulfoxide reductase is important for the gastric pathogen Helicobacter pylori to maintain persistent stomach colonization. Methionine-containing proteins that are targeted for repair by Msr were identified from whole-cell extracts (after cells were exposed to O2 stress) by using a coimmunoprecipitation approach. Proteins identified as Msr-interacting included catalase, GroEL, thioredoxin-1 (Trx1), and site-specific recombinase; with one exception (Trx1, the reductant for Msr) all these proteins have approximately twofold higher methionine (Met) content than other proteins. These Met-rich proteins were purified and were shown to individually form a cross-linked adduct with Msr. Catalase-specific activity in an msr strain was one-half that of the parent strain; this difference was only observed under oxidative stress conditions, and the activity was restored to nearly wild-type levels by adding Msr plus dithiothreitol to msr strain extracts. In agreement with the cross-linking study, pure Msr used Trx1 but not Trx2 as a reductant. Comparative structure modeling classified the H. pylori Msr in class II within the MsrB family, like the Neisseria enzymes. Pure H. pylori enzyme reduced only the R isomer of methyl p-tolyl-sulfoxide with an apparent Km of 4.1 mM for the substrate. Stress conditions (peroxide, peroxynitrite, and iron starvation) all caused approximately 3- to 3.5-fold transcriptional up-regulation of msr. Neither the O2 level during growth nor the use of background regulatory mutants had a significant effect on msr transcription. Late log and stationary phase cultures had the highest Msr protein levels and specific activity.

* Corresponding author. Mailing address: Department of Microbiology, The University of Georgia, Biological Sciences Bldg., 527, 1000 Cedar Street, Athens, GA 30602. Phone: (706) 542-2323. Fax: (706) 542-2674. E-mail: rmaier{at}uga.edu.

Journal of Bacteriology, August 2006, p. 5839-5850, Vol. 188, No. 16
0021-9193/06/$08.00+0     doi:10.1128/JB.00430-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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