Purified components of the Escherichia coli Tat protein transport system form a double-layered ring structure

Authors

  • Frank Sargent,

    1. Centre for Metalloprotein Spectroscopy and Biology, School of Biological Sciences, University of East Anglia, Norwich, UK;
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  • Ulrich Gohlke,

    1. Bloomsbury Centre for Structural Biology, Birkbeck College, Department of Crystallography, London, UK;
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  • Erik de Leeuw,

    1. Centre for Metalloprotein Spectroscopy and Biology, School of Biological Sciences, University of East Anglia, Norwich, UK;
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  • Nicola R. Stanley,

    1. Centre for Metalloprotein Spectroscopy and Biology, School of Biological Sciences, University of East Anglia, Norwich, UK;
    2. Department of Molecular Microbiology, John Innes Centre, Norwich Research Park, Norwich, UK.
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  • Tracy Palmer,

    1. Centre for Metalloprotein Spectroscopy and Biology, School of Biological Sciences, University of East Anglia, Norwich, UK;
    2. Department of Molecular Microbiology, John Innes Centre, Norwich Research Park, Norwich, UK.
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  • Helen R. Saibil,

    1. Bloomsbury Centre for Structural Biology, Birkbeck College, Department of Crystallography, London, UK;
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  • Ben C. Berks

    1. Centre for Metalloprotein Spectroscopy and Biology, School of Biological Sciences, University of East Anglia, Norwich, UK;
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B. C. Berks, School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK. Fax: + 44 1603 592250, Tel.: + 44 1603 592186, E-mail: b.berks@uea.ac.uk

Abstract

The Escherichia coli twin arginine translocation (Tat) system mediates Sec-independent export of protein precursors bearing twin arginine signal peptides. The genes tatA, tatB, tatC and tatE code for integral membrane proteins that are components of the Tat pathway. Cells co-overexpressing tatABCDE show an increased rate of export of a signal peptide-defective Tat precursor protein and a complex containing the TatA and TatB proteins can be purified from the membranes of such cells. The purified TatAB complex has an apparent molecular mass of 600 kDa as measured by gel permeation chromatography and, like the membranes of wild-type cells, contains a large molar excess of TatA over TatB. Negative stain electron microscopy of the complex reveals cylindrical structures that may correspond to the Tat protein transport channel.

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