pH Regulation of Electrogenic Sugar/H+ Symport in MFS Sugar Permeases.
pH Regulation of Electrogenic Sugar/H+ Symport in MFS Sugar Permeases.
复制标题
MFS糖磁盘中的电糖/H+同步的pH调节。
DOI：
10.1371/journal.pone.0156392
复制
发表时间：
2016
期刊：
影响因子：
3.7
通讯作者：
Fendler K
中科院分区：
文献类型：
--
作者：
Bazzone A;Madej MG;Kaback HR;Fendler K
主要促进剂超家族(MFS)中的细菌糖转运体利用H+(在少数情况下还包括Na+)电化学梯度来实现糖的主动转运到细胞内。由于最近已经解决了MFS糖转运体的许多结构，通过详细的功能分析可以从分子上深入了解MFS糖转运体的转运机制。我们对乳糖渗透酶(Lacy)、岩藻糖渗透酶(FucP)和木糖渗透酶(XylE)进行了比较电生理学研究，揭示了共同的机制原理和差异。在这三个共转运体中，都观察到了能量下坡的生糖/H+共转运体。在对称pH条件下，Symport的pH依赖关系的比较显示，在3~6个pH单位范围内呈钟形分布，在极碱性pH≥9.4时和在酸性到中性pH=4.67.5时下降。PH依赖性可以用酸性到中性的表观pK(PKapp)和碱性的pKapp来描述。实验证据表明，碱性的pKapp是由于质子化中心的H+耗尽，而酸性的pKapp是由于抑制了去质子化。由于先前的研究表明，Lacy(Glu325)上的一个羧基可能是唯一直接参与H+转运的侧链，而在FucP(Asp46)和XylE(Asp27)中也发现了一个性质相似的羧基侧链，因此本研究结果表明，在这三个共转运体中，该残基的pK在H+/糖结合过程中发生了转换。
Bacterial sugar symporters in the Major Facilitator Superfamily (MFS) use the H+ (and in a few cases Na+) electrochemical gradients to achieve active transport of sugar into the cell. Because a number of structures of MFS sugar symporters have been solved recently, molecular insight into the transport mechanism is possible from detailed functional analysis. We present here a comparative electrophysiological study of the lactose permease (LacY), the fucose permease (FucP) and the xylose permease (XylE), which reveals common mechanistic principles and differences. In all three symporters energetically downhill electrogenic sugar/H+ symport is observed. Comparison of the pH dependence of symport at symmetrical pH exhibits broad bell-shaped pH profiles extending over 3 to 6 pH units and a decrease at extremely alkaline pH ≥ 9.4 and at acidic to neutral pH = 4.6–7.5. The pH dependence can be described by an acidic to neutral apparent pK (pKapp) and an alkaline pKapp. Experimental evidence suggests that the alkaline pKapp is due to H+ depletion at the protonation site, while the acidic pKapp is due to inhibition of deprotonation. Since previous studies suggest that a single carboxyl group in LacY (Glu325) may be the only side chain directly involved in H+ translocation and a carboxyl side chain with similar properties has been identified in FucP (Asp46) and XylE (Asp27), the present results imply that the pK of this residue is switched during H+/sugar symport in all three symporters.