A matter of life and death: cell wall homeostasis and the WalKR (YycGF) essential signal transduction pathway

Authors

  • Sarah Dubrac,

    1. Biology of Gram-Positive Pathogens, CNRS URA 2172, Department of Microbiology, Institut Pasteur, 25, Rue du Dr Roux, 75724 Paris Cedex 15, France.
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    • The first two authors contributed equally to this work.

  • Paola Bisicchia,

    1. Smurfit Institute of Genetics, Trinity College Dublin, Dublin 2, Ireland.
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    • The first two authors contributed equally to this work.

  • Kevin M. Devine,

    Corresponding author
    1. Smurfit Institute of Genetics, Trinity College Dublin, Dublin 2, Ireland.
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  • Tarek Msadek

    Corresponding author
    1. Biology of Gram-Positive Pathogens, CNRS URA 2172, Department of Microbiology, Institut Pasteur, 25, Rue du Dr Roux, 75724 Paris Cedex 15, France.
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*E-mail tmsadek@pasteur.fr; Tel. (33)-1-45-68-88-09; Fax (33)-1-45-68-89-38.

**E-mail kdevine@tcd.ie; Tel. (353)-1-896 1872; Fax (353)-1-671 4968.

Summary

The WalK/WalR (aka YycG/YycF) two-component system (TCS), originally identified in Bacillus subtilis, is very highly conserved and specific to low G+C Gram-positive bacteria, including a number of important pathogens. An unusual feature is that this system is essential for viability in most of these bacteria. Recent studies have revealed conserved functions for this system, defining this signal transduction pathway as a crucial regulatory system for cell wall metabolism, that we have accordingly renamed WalK/WalR. Here we review the cellular role of the WalK/WalR TCS in different bacterial species, focusing on the function of genes in its regulon, as well as variations in walRK operon structure and the composition of its regulon. We also discuss the nature of its essentiality and the potential type of signal being sensed. The WalK histidine kinase of B. subtilis has been shown to localize to the divisome and we suggest that the WalKR system acts as an information conduit between extracytoplasmic cellular structures and intracellular processes required for their synthesis, playing a vital role in effectively co-ordinating peptidoglycan plasticity with the cell division process.

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