Download MendeleyEscherichia coli acid resistance: pH-sensing, activation by chloride and autoinhibition in GadB
Gut, H., Pennacchietti, E., John, R.A., Bossa, F., Capitani, G., De Biase, D., Gruetter, M.G.(2006) EMBO J 25: 2643-2651
- PubMed: 16675957
- DOI: https://doi.org/10.1038/sj.emboj.7601107
- Primary Citation of Related Structures:
2DGK, 2DGL, 2DGM - PubMed Abstract:
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.
Organizational Affiliation:
Biochemisches Institut der Universität Zürich, Zürich, Switzerland.
