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. Tetracycline; Antiporter; Serine; Tetracycline/H+ antiporter; Site-directed mutagenesis; Antibiotic resistance. © 1992.
Yamaguchi, A., Ono, N., Akasaka, T., & Sawai, T. (1992). 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. FEBS Letters, 307(2), 229–232. https://doi.org/10.1016/0014-5793(92)80773-A