Serine residues responsible for tetracycline transport are on a vertical stripe including Asp-84 on one side of transmembrane helix 3 in transposon Tn10-encoded tetracycline/H+ antiporter of Escherichia coli.
Putative transmembrane helix 3 of the tetracycline/H+ antiporter encoded by a transposon, Tn10, contains four serine residues, Ser-77, Ser-82, Ser-91 and Ser-92. Each of these serine residues was replaced by site-directed mutagenesis. Of these four serine residues, Ser-77 was important for the transport function, and a bulky side chain at position 91 hindered substrate translocation, whereas Ser-82 and Ser-92 did not play any role. Ser-77 and Ser-91 are on the same vertical stripe, that includes the essential Asp-84, on the hydrophilic side of putative helix 3. These observations suggest that helix 3 is part of the tetracycline translocation channel across the membrane.
Yamaguchi
A
A
Division of Microbial Chemistry, Faculty of Pharmaceutical Sciences, Chiba University, Japan.
Ono
N
N
Akasaka
T
T
Sawai
T
T
D000409:Alanine / Q000378:metabolism; D000595:Amino Acid Sequence; D017920:Antiporters; D001224:Aspartic Acid / Q000378:metabolism; D001426:Bacterial Proteins; D001483:Base Sequence; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D003545:Cysteine / Q000378:metabolism; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D015151:Immunoblotting; D007700:Kinetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism; D012694:Serine / Q000378:metabolism*; D013752:Tetracycline / Q000737:chemistry / Q000378:metabolism*; D013912:Threonine / Q000378:metabolism
D017920:Antiporters; D001426:Bacterial Proteins; D002352:Carrier Proteins; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D012097:Repressor Proteins; C079051:tetA protein, Bacteria; D013912:Threonine; D001224:Aspartic Acid; D012694:Serine; D013752:Tetracycline; D003545:Cysteine; D000409:Alanine