Journal
JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 288, Issue 21, Pages 15148-15153Publisher
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M113.474502
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Funding
- Ministry of Science and Technology 973 Program Grant [2009CB918801]
- National Natural Science Foundation of China [30888001, 31021002, 31130002]
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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. AC-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 similar to 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.
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