2DGL: Crystal Structure of Escherichia Coli Gadb in Complex With Bromide

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.
PDB ID: 2DGLDownload
MMDB ID: 39792
PDB Deposition Date: 2006/3/14
Updated in MMDB: 2007/10 
Experimental Method:
x-ray diffraction
Resolution: 3.15  Å
Source Organism:
Similar Structures:
Biological Unit for 2DGL: hexameric; determined by author and by software (PISA)
Molecular Components in 2DGL
Label Count Molecule
Proteins (6 molecules)
Glutamate Decarboxylase Beta
Molecule annotation
Chemicals (36 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB