Involved in glutaminase-dependent acid resistance (PubMed:9484886). Exchanges extracellular glutamate (Glu) for intracellular gamma-aminobutyric acid (GABA) under acidic conditions (By similarity). 4-aminobutanoate(in) + L-glutamate(out) = 4-aminobutanoate(out) + L-glutamate(in) Expression is highest at onset of stationary phase in presence of NaCl and glutamate, and at low pH. Chloride-dependent expression is activated by GadR. Belongs to the amino acid-polyamine-organocation (APC) superfamily. Glutamate:GABA antiporter (GGA) (TC 2.A.3.7) family.