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  • The EMBO Journal (2006) 25, 2643 - 2651
  • doi:10.1038/sj.emboj.7601107

Published online: 4 May 2006

Escherichia coli acid resistance: pH-sensing, activation by chloride and autoinhibition in GadB

Heinz Gut1, Eugenia Pennacchietti2, Robert A John3, Francesco Bossa2,4,5, Guido Capitani1, Daniela De Biase2,4,5 and Markus G Grütter1

  1. Biochemisches Institut der Universität Zürich, Zürich, Switzerland
  2. Dipartimento di Scienze Biochimiche, Università di Roma La Sapienza, Roma, Italy
  3. School of Biosciences, Cardiff University, Cardiff, UK
  4. Centro di Eccellenza di Biologia e Medicina Molecolare, Università di Roma La Sapienza, Roma, Italy
  5. This paper is dedicated to the memory of Professor Giorgio Tecce

Correspondence to:

Daniela De Biase, Dipartimento di Scienze Biochimiche, Università di Roma La Sapienza, Roma 00185, Italy. Tel.: +39 06 49917692; Fax: +39 06 49917566; E-mail: daniela.debiase@uniroma1.it

Guido Capitani, Biochemisches Institut, Universität Zürich, Winterthurerstrasse 190, Zürich, Switzerland. Tel.: +41 44 635 55 87; Fax: +41 44 635 68 34; E-mail: capitani@bioc.unizh.ch

Received 30 December 2005; Accepted 27 March 2006

Escherichia coli and other enterobacteria exploit the H+-consuming reaction catalysed by glutamate decarboxylase to survive the stomach acidity before reaching the intestine. Here we show that chloride, extremely abundant in gastric secretions, is an allosteric activator producing a 10-fold increase in the decarboxylase activity at pH 5.6. Cooperativity and sensitivity to chloride were lost when the N-terminal 14 residues, involved in the formation of two triple-helix bundles, were deleted by mutagenesis. X-ray structures, obtained in the presence of the substrate analogue acetate, identified halide-binding sites at the base of each N-terminal helix, showed how halide binding is responsible for bundle stability and demonstrated that the interconversion between active and inactive forms of the enzyme is a stepwise process. We also discovered an entirely novel structure of the cofactor pyridoxal 5'-phosphate (aldamine) to be responsible for the reversibly inactivated enzyme. Our results link the entry of chloride ions, via the H+/Cl- exchange activities of ClC-ec1, to the trigger of the acid stress response in the cell when the intracellular proton concentration has not yet reached fatal values.

  • Keywords:

    • autoinhibition,
    • bacterial acid resistance,
    • chloride binding,
    • glutamate decarboxylase,
    • pyridoxal 5'-phosphate