Liu M, Turner R J, Winstone T L, Saetre A, Dyllick-Brenzinger M, Jickling G, Tari L W, Weiner J H, Taylor D E
Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
J Bacteriol. 2000 Nov;182(22):6509-13. doi: 10.1128/JB.182.22.6509-6513.2000.
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 K(2)TeO(3) at 128 microg/ml, compared to the MIC of 2 microg/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 approximately 20% decrease upon binding of both tellurite and SAM. These data suggest that TehB utilizes a methyltransferase activity in the detoxification of tellurite.
大肠杆菌对亚碲酸盐抗性的染色体决定因素由两个基因（tehA和tehB）组成，当这两个基因在多拷贝质粒上表达时，与野生型2微克/毫升的最低抑菌浓度相比，可赋予对128微克/毫升K(2)TeO(3)的抗性。TehB是一种细胞质蛋白，具有在依赖S-腺苷-L-甲硫氨酸（SAM）的非核酸甲基转移酶中发现的三个保守基序（I、II和III）。将基序I中保守的天冬氨酸残基替换为天冬酰胺或丙氨酸，或将基序II中保守的苯丙氨酸替换为酪氨酸或丙氨酸，会使抗性降至背景水平。我们的结果与TehB中的基序I和II参与SAM结合一致。此外，在亚碲酸盐和SAM结合时均观察到TehB的构象变化。通过动态光散射测量，TehB的流体动力学半径在亚碲酸盐和SAM结合时均显示出约20%的减小。这些数据表明TehB在亚碲酸盐解毒过程中利用了甲基转移酶活性。
