Ginn S L, Brown M H, Skurray R A
School of Biological Sciences, University of Sydney, Sydney, New South Wales 2006, Australia.
J Bacteriol. 2000 Mar;182(6):1492-8. doi: 10.1128/JB.182.6.1492-1498.2000.
Conserved motif C, identified within members of the major facilitator superfamily (MFS) of transport proteins that mediate drug export, was examined in the tetracycline resistance efflux protein TetA(K) from Staphylococcus aureus; motif C is contained within transmembrane segment 5. Using site-directed mutagenesis, the importance of the conserved glycine (G151, G155, G159, and G160) and proline (P156) residues within this motif was investigated. Over 40 individual amino acid replacements were introduced; however, only alanine and serine substitutions for glycine at G151, G155, and G160 were found to retain significant levels of tetracycline resistance and transport activity in cells expressing mutant proteins. Notably, P156 and G159 appear to be crucial, as amino acid replacements at these positions either significantly reduced or abolished tetracycline/H(+) activity. The highly conserved nature of motif C and its distribution throughout drug exporters imply that the residues of motif C play a similar role in all MFS proteins that function as antiporters.
保守基序C是在介导药物外排的转运蛋白主要易化子超家族（MFS）成员中鉴定出来的，本研究对金黄色葡萄球菌的四环素抗性外排蛋白TetA(K)中的保守基序C进行了检测；基序C包含在跨膜区段5内。利用定点诱变技术，研究了该基序中保守的甘氨酸（G151、G155、G159和G160）和脯氨酸（P156）残基的重要性。引入了40多个单个氨基酸替换；然而，在表达突变蛋白的细胞中，仅发现G151、G155和G160处的甘氨酸被丙氨酸和丝氨酸替换后仍保留显著水平的四环素抗性和转运活性。值得注意的是，P156和G159似乎至关重要，因为这些位置的氨基酸替换显著降低或消除了四环素/H(+)活性。基序C的高度保守性质及其在整个药物外排蛋白中的分布表明，基序C的残基在所有作为反向转运体发挥作用的MFS蛋白中起着类似的作用。
