Escherichia coliTehB RequiresS-Adenosylmethionine as a Cofactor To Mediate Tellurite Resistance

Abstract

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 K 2 TeO 3 at 128 g/ml, compared to the MIC of 2 g/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 ϳ20% decrease upon binding of both tellurite and SAM. These data suggest that TehB utilizes a methyltransferase activity in the detoxification of tellurite.Tellurite (TeO 3 2Ϫ ) resistance, which is found in many microorganisms (37), is carried on plasmids of IncHI, IncHII, and IncP incompatibility groups (3, 36, 39) and/or on chromosomes (9, 10, 29, 33). Tellurite resistance (Te r ) determinants are very diverse, and at least five different determinants have been identified (37). Te r determinants are unrelated, and probably different resistance mechanisms are involved. Except for that encoded by the Pseudomonas syringae tpm gene, Te r mechanisms are not clearly understood. tpm encodes a methyltransferase that catalyzes S-adenosyl-L-methionine (SAM) methylation of 6-mercaptopurine, a substrate for human thiopurine methyltransferase. It was assumed that tellurite is also a substrate for this enzyme (11).The Te r determinant tehAB, an operon located at 32.3 min on the Escherichia coli K-12 chromosome (38), encodes proteins of 330 (TehA) and 197 (TehB) amino acids. TehA is a membrane protein with 10 transmembrane segments, whereas TehB is a soluble protein. The closest homologues of these two genes are found in Haemophilus influenzae (15).A sequence search performed with the BLAST program (National Center for Biotechnology Information), followed by alignment analysis with the Genetics Computer Group software package (University of Wisconsin) (12), demonstrated that TehB displays some amino acid sequence similarity to many SAM-dependent non-nucleic acid methyltransferases. These proteins have three shared motifs, and the TehB proteins show homologies within all regions with comparable sequence interval distances (Fig.

Site-Directed Mutagenesis as a Tool for Unveiling Mechanisms of Bacterial Tellurite Resistance

“…Thus, a putative role of SUMT in K 2 TeO 3 resistance would be the utilization of Te as a substrate and to catalyze the transfer of methyl groups from SAM to the metalloid. In this context, some work from other authors has indicated that the gene products of the tpm and tehB genes from Pseudomonas syringae and E. coli, respectively, are able to biomethylate tellurium (Cournoyer et al, 1998;Liu et al, 2000). Unfortunately, we were unable to detect the genesis of methylated tellurium derivatives in the headspace of cells cultured in the presence of tellurite or tellurate.…”

Activation of yeaR-yoaG Operon Transcription by the Nitrate-Responsive Regulator NarL Is Independent of Oxygen- Responsive Regulator Fnr in Escherichia coli K-12

“…In other species, the YeaR domain is present as an aminoterminal extension in homologs of the E. coli TehB protein, an S-adenosylmethionine-dependent non-nucleic acid methyltransferase involved in resistance to tellurite (28). This YeaRTehB fusion protein is annotated as "TehB" in several genome sequences (e.g., locus tag YPTB1947 in Y. pseudotuberculosis IP32953 and locus tag spr0880 in S. pneumoniae R6).…”

Genome-Wide Transcriptional Profiling of the Purple Sulfur Bacterium Allochromatium vinosum DSM 180T during Growth on Different Reduced Sulfur Compounds

“…The kanamycin ⍀ cassette replacing Alvin_3072 therefore most likely also prevents formation of the Alvin_3073-encoded transporter, and more experiments are needed to exactly dissect the effect exerted by the interposon. The protein Alvin_3073 belongs to a family of transporters that includes a malate uptake system in the yeast Schizosaccharomyces pombe (63), a tellurite resistance protein in Escherichia coli (64), and notably, a sulfite efflux pump in Saccharomyces cerevisiae and other fungi, including Aspergillus fumigatus (65). Alvin_3072 is conserved in several sulfide-oxidizing bacteria (see Fig.…”