Relaxases and Plasmid Transfer in Gram-Negative Bacteria

  • Ellen L. ZechnerEmail author
  • Gabriel Moncalián
  • Fernando de la Cruz
Part of the Current Topics in Microbiology and Immunology book series (CT MICROBIOLOGY, volume 413)


All plasmids that spread by conjugative transfer encode a relaxase. That includes plasmids that encode the type IV secretion machinery necessary to mediate cell to cell transfer, as well as mobilizable plasmids that exploit the existence of other plasmids’ type IV secretion machinery to enable their own lateral spread. Relaxases perform key functions in plasmid transfer by first binding to their cognate plasmid as part of a multiprotein complex called the relaxosome, which is then specifically recognized by a receptor protein at the opening of the secretion channel. Relaxases catalyze a site- and DNA-strand-specific cleavage reaction on the plasmid then pilot the single strand of plasmid DNA through the membrane-spanning type IV secretion channel as a nucleoprotein complex. In the recipient cell, relaxases help terminate the transfer process efficiently and stabilize the incoming plasmid DNA. Here, we review the well-studied MOBF family of relaxases to describe the biochemistry of these versatile enzymes and integrate current knowledge into a mechanistic model of plasmid transfer in Gram-negative bacteria.


Bacterial conjugation Bacterial type IV secretion Conjugative DNA processing Relaxase DNA helicase Plasmid 



Work in the authors’ laboratories was supported by Austrian Science Fund (FWF) grants P24016 and W901 DK Molecular Enzymology (ELZ) and BioTechMed-Graz (ELZ) and by the Spanish Ministry of Economy and Competitiveness grants BFU2014-55534-C2-1-P (FdlC) and BFU2014-55534-C2-2-P (GM).


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© Springer International Publishing AG 2017

Authors and Affiliations

  • Ellen L. Zechner
    • 1
    Email author
  • Gabriel Moncalián
    • 2
  • Fernando de la Cruz
    • 2
  1. 1.Institute of Molecular Biosciences, University of GrazGrazAustria
  2. 2.Departamento de Biología MolecularUniversidad de Cantabria and Instituto de Biomedicina y Biotecnología de Cantabria (IBBTEC), Consejo Superior de Investigaciones Científicas—Universidad de CantabriaSantanderSpain

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