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Journal of Bacteriology, November 2000, p. 6509-6513, Vol. 182, No. 22
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Escherichia coli TehB Requires S-Adenosylmethionine as a Cofactor To Mediate Tellurite Resistance

Mingfu Liu,1 Raymond J. Turner,2,* Tara L. Winstone,2 Andrea Saetre,2 Melanie Dyllick-Brenzinger,2 Glen Jickling,2 Leslie W. Tari,2 Joel H. Weiner,3 and Diane E. Taylor1

Department of Medical Microbiology and Immunology1 and Department of Biochemistry,3 University of Alberta, Edmonton, Alberta T6G 2H7, and Structural Biology Research Group, Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4,2 Canada

Received 30 May 2000/Accepted 1 September 2000

The Escherichia coli chromosomal determinant for tellurite resistance consists of two genes (tehA and tehB) which, when expressed on a multicopy plasmid, confer resistance to K2TeO3 at 128 µg/ml, compared to the MIC of 2 µg/ml for the wild type. TehB is a cytoplasmic protein which possesses three conserved motifs (I, II, and III) found in S-adenosyl-L-methionine (SAM)-dependent non-nucleic acid methyltransferases. Replacement of the conserved aspartate residue in motif I by asparagine or alanine, or of the conserved phenylalanine in motif II by tyrosine or alanine, decreased resistance to background levels. Our results are consistent with motifs I and II in TehB being involved in SAM binding. Additionally, conformational changes in TehB are observed upon binding of both tellurite and SAM. The hydrodynamic radius of TehB measured by dynamic light scattering showed a ~20% decrease upon binding of both tellurite and SAM. These data suggest that TehB utilizes a methyltransferase activity in the detoxification of tellurite.

* Corresponding author. Mailing address: Department of Biological Sciences, University of Calgary, 2500 University Dr. N.W., Calgary, Alberta T2N 1N4, Canada. Phone: (403) 220-4308. Fax: (403) 289-9311. E-mail: turnerr{at}ucalgary.ca.

Journal of Bacteriology, November 2000, p. 6509-6513, Vol. 182, No. 22
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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