A novel membrane-associated threonine permease encoded by the tdcC gene of Escherichia coli.
A novel L-threonine transport system is induced in Escherichia coli cells when incubated in amino acid-rich medium under anaerobic conditions. Genetic and biochemical analyses with plasmids harboring mutations in the anaerobically expressed tdcABC operon indicated that the tdcC gene product was responsible for L-threonine uptake. Competition experiments revealed that the L-threonine transport system is also involved in L-serine uptake and is partially shared for L-leucine transport; L-alanine, L-valine, and L-isoleucine did not affect L-threonine uptake. Transport of L-threonine was inhibited by the respiratory chain inhibitors KCN and carbonyl cyanide m-chlorophenylhydrazone and was Na+ independent. These results identify for the first time an E. coli gene encoding a permease specific for L-threonine-L-serine transport that is distinct from the previously described threonine-serine transport systems. A two-dimensional topological model predicted from the amino acid composition and hydropathy plot showed that the TdcC polypeptide appears to be an integral membrane protein with several membrane-spanning domains exhibiting a striking similarity with other bacterial permeases.
Sumantran
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Department of Biological Chemistry, University of Michigan, Ann Arbor 48109-0606.
Schweizer
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Datta
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D000595:Amino Acid Sequence; D026921:Amino Acid Transport Systems, Neutral; D000596:Amino Acids / Q000494:pharmacology; D001483:Base Sequence; D001692:Biological Transport / Q000187:drug effects; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002462:Cell Membrane / Q000201:enzymology / Q000648:ultrastructure; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics*; D029968:Escherichia coli Proteins; D005798:Genes, Bacterial; D007700:Kinetics; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D008961:Models, Structural; D008969:Molecular Sequence Data; D009876:Operon; D010957:Plasmids; D011190:Potassium Cyanide / Q000494:pharmacology; D011487:Protein Conformation; D015183:Restriction Mapping; D013912:Threonine / Q000378:metabolism; D013913:Threonine Dehydratase / Q000378:metabolism
D026921:Amino Acid Transport Systems, Neutral; D000596:Amino Acids; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; C065101:tdcC protein, E coli; D013912:Threonine; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D013913:Threonine Dehydratase; D011190:Potassium Cyanide