Substrate selectivity of the acid-activated glutamate/γ-aminobutyric acid (GABA) antiporter GadC from Escherichia coli

J Biol Chem. 2013 May 24;288(21):15148-53. doi: 10.1074/jbc.M113.474502. Epub 2013 Apr 15.


GadC, a central component of the Escherichia coli acid resistance system, is a Glu/GABA antiporter. A previous structural study and biochemical characterization showed that GadC exhibits a stringent pH dependence for substrate transport, with no detectable activity at pH values above 6.5. However, the substrate selectivity and the mechanism of pH-dependent transport activity of GadC remain enigmatic. In this study, we demonstrate that GadC selectively transports Glu with no net charge and GABA with a positive charge. A C-plug-truncated variant of GadC (residues 1-470) transported Gln (a mimic of Glu with no net charge), but not Glu, even at pH 8.0. The pH-dependent transport of Gln by this GadC variant was shifted ~1 unit toward a higher pH compared with Glu transport. Taken together, the results identify the substrate selectivity for GadC and show that the protonation states of substrates are crucial for transport.

Keywords: Acid Resistance; Amino Acid Transport; GadC; Glutamate; Glutamine; Membrane Antiporter; Membrane Proteins; Membrane Transporter Reconstitution; Protonation/Deprotonation; Substrate Selectivity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biological Transport, Active / physiology*
  • Escherichia coli / genetics
  • Escherichia coli / metabolism*
  • Escherichia coli Proteins / genetics
  • Escherichia coli Proteins / metabolism*
  • Glutamine / genetics
  • Glutamine / metabolism*
  • Hydrogen-Ion Concentration
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Substrate Specificity / physiology


  • Escherichia coli Proteins
  • GadC protein, E coli
  • Membrane Proteins
  • Glutamine