biostudies-literatureUnknown288(21)Ma DGadC, 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.The Journal of biological chemistry15148-53https://www.ebi.ac.uk/biostudies/studies/S-EPMC3663535biostudies-literatureSubstrate selectivity of the acid-activated glutamate/γ-aminobutyric acid (GABA) antiporter GadC from Escherichia coli.PMC3663535Ma DLu PShi YfalseSubstrate selectivity of the acid-activated glutamate/γ-aminobutyric acid (GABA) antiporter GadC from Escherichia coli.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.2013-01-01T00:00:00Z2013 May2025-04-04T23:39:29.81Z2019-03-27T01:10:22ZS-EPMC36635352358930910.1074/jbc.M113.474502