Multidrug resistance protein MdtM adds to the repertoire of antiporters involved in alkaline pH homeostasis in Escherichia coli.
Multidrug resistance protein MdtM adds to the repertoire of antiporters involved in alkaline pH homeostasis in Escherichia coli.
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DOI：
10.1186/1471-2180-13-113
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发表时间：
2013-05-23
期刊：
影响因子：
4.2
通讯作者：
Law CJ
中科院分区：
文献类型：
--
作者：
Holdsworth SR;Law CJ
在嗜中性细菌中，单价金属阳离子/H+反向转运蛋白在pH稳态中起关键作用。在大肠杆菌中，只有四个反向转运蛋白（NhaA，NhaB，MdfA和ChaA）被确定为在碱性胁迫条件下维持稳定的细胞质pH值的功能。我们假设，多药耐药蛋白MdtM，最近表征的同源物MdfA和一个成员的主要促进超家族，也在碱性pH值的稳态功能。比较了E.用编码野生型MdtM或功能失调的MdtM D22 A突变体的质粒转化的大肠杆菌ΔmdtM缺失突变体在不同的外部碱性pH值（pH 8.5 - 10）下显示MdtM对碱性pH耐受性的潜在贡献，但仅当生长培养基中存在毫摩尔浓度的钠或钾时。使用从antiporter缺陷型（ΔnhaA，ΔnhaB，ΔchaA）E的转化体产生的倒置囊泡进行的基于生物活性的测定。coliTO 114细胞将MdtM定义为低亲和力的反向转运蛋白，其催化Na+、K+、Rb+或Li+与H+的产电交换。K+/H+逆向转运反应的最适pH为9.0，而Na+/H+交换活性的最适pH为9.25。内部细胞pH值的测量证实MdtM有助于维持一个稳定的细胞质pH值，酸性相对于外部pH值，在碱性胁迫条件下。总之，结果支持MdtM在碱性pH耐受性中的作用。因此，MdtM可以被添加到目前有限的已知在模式生物E中的pH稳态中起作用的反向转运蛋白的列表中。杆菌
In neutralophilic bacteria, monovalent metal cation/H+ antiporters play a key role in pH homeostasis. In Escherichia coli, only four antiporters (NhaA, NhaB, MdfA and ChaA) are identified to function in maintenance of a stable cytoplasmic pH under conditions of alkaline stress. We hypothesised that the multidrug resistance protein MdtM, a recently characterised homologue of MdfA and a member of the major facilitator superfamily, also functions in alkaline pH homeostasis. Assays that compared the growth of an E. coli ΔmdtM deletion mutant transformed with a plasmid encoding wild-type MdtM or the dysfunctional MdtM D22A mutant at different external alkaline pH values (ranging from pH 8.5 to 10) revealed a potential contribution by MdtM to alkaline pH tolerance, but only when millimolar concentrations of sodium or potassium was present in the growth medium. Fluorescence-based activity assays using inverted vesicles generated from transformants of antiporter-deficient (ΔnhaA, ΔnhaB, ΔchaA) E. coli TO114 cells defined MdtM as a low-affinity antiporter that catalysed electrogenic exchange of Na+, K+, Rb+ or Li+ for H+. The K+/H+ antiport reaction had a pH optimum at 9.0, whereas the Na+/H+ exchange activity was optimum at pH 9.25. Measurement of internal cellular pH confirmed MdtM as contributing to maintenance of a stable cytoplasmic pH, acid relative to the external pH, under conditions of alkaline stress. Taken together, the results support a role for MdtM in alkaline pH tolerance. MdtM can therefore be added to the currently limited list of antiporters known to function in pH homeostasis in the model organism E. coli.
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影响因子：
2.7
作者：
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通讯作者：
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