The role of cysteine residues in the transport of mercuric ions by the Tn501 MerT and MerP mercury-resistance proteins

Authors

  • Andrew P. Morby,

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    • *For correspondence. E-mail A.P.MORBY@BHAM. AC.UK; Tel. (021) 4146567; Fax (021) 4146557.

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  • Jon L. Hobman,

    1. Microbial Molecular Genetics and Cell Biology Group, School of Biological Sciences, The University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
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  • Nigel L. Brown

    1. Microbial Molecular Genetics and Cell Biology Group, School of Biological Sciences, The University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
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Abstract

Each cysteine residue in the MerT and MerP polypeptides of bacterial transposon Tn501 was replaced by serine, and the mercury-resistance phenotypes of the mutants were determined in Escherichia coli. Cys−24 and Cys−25 in the first transmembrane region of MerT were essential for transport of mercuric ions through the cytoplasmic membrane, and mutations Cys−76-Ser, Cys−82-Ser or Gly−38-Asp in MerT or Cys−36-Ser in MerP all reduced transport and resistance. Deletion of the merP gene slightly reduced mercuric ion resistance and transport, whereas a Cys−33-Ser mutation in MerP appears to block transport of mercuric ions by MerT. The effects of deleting merP on mutations in merT were tested. The 116-amino-acid MerT protein is sufficient for mercuric ion transport across the cytoplasmic membrane.

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