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Cation‐selectivity of the l ‐glutamate transporters of Escherichia coli, Bacillus stearothermophilus and Bacillus caldotenax : dependence on the environment in which the proteins are expressed
Author(s) -
Tolner Berend,
UbbinkKok Trees,
Poolmann Bert,
Konings Wil N.
Publication year - 1995
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.1995.mmi_18010123.x
Subject(s) - symporter , biology , escherichia coli , bacillus (shape) , biochemistry , bacillus subtilis , bacillales , transporter , bacillaceae , glutamate receptor , membrane transport , bacteria , membrane , microbiology and biotechnology , gene , genetics , receptor
l ‐Glutamate transport by the H + ‐glutamate and Na + ‐glutamate symport proteins of Escherichia coli K‐12 (GltP Ec and GltS Ec , respectively) and the Na + ‐H + ‐glutamate symport proteins of Bacillus stearothermophilus (GltT Bs ) and Bacillus caldotenax (GltT Bc ) was studied in membrane vesicles derived from cells in which the proteins were either homologously or heterologously expressed. Substrate and inhibitor specificity studies indicate that GltP Ec , GltT Bs and GltT Bc fall into the same group of transporters, whereas GltS Ec is distinctly different from the others. Also, the cation specificity of GltS Ec is different; GltS Ec transported l ‐glutamate with (at least) two Na + , whereas GltP Ec , GltT Bs and GltT Bc catalysed an electrogenic symport of l ‐glutamate with ≥two H + , i.e. when the proteins were expressed in E. coli Surprisingly studies in membrane vesicles of B. stearothermophilus and B. caldotenax indicated a Na + ‐H + ‐ l ‐glutamate symport for both GltT Bs and GltT Bc . The Na + dependency of the GltT transporters in the Bacillus strains increased with temperature. These observations suggest that the conformation of the transport proteins in the E. coli and the Bacillus membranes differs, which influences the coupling ion selectivity.