Membrane-integral pyrophosphatase subfamily capable of translocating both Na+ and H+
Membrane-integral pyrophosphatase subfamily capable of translocating both Na+ and H+
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DOI：
10.1073/pnas.1217816110
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发表时间：
2013-01-22
影响因子：
11.1
通讯作者：
Malinen, Anssi M.
中科院分区：
文献类型：
--
作者：
Luoto, Heidi H.;Baykov, Alexander A.;Malinen, Anssi M.
生物体在能量供应不足的条件下适应生活的策略之一是利用副产物焦磷酸盐来支持膜中的阳离子梯度。转运反应由膜整合焦磷酸酶（PPases）催化，PPases分为两个同源的亚家族：H+转运（在原核生物、原生生物和植物中发现）和Na+转运（在原核生物中发现）。运输活动已被认为需要特定的机器为每个离子，根据在膜运输的流行范式。然而，当前研究中使用荧光pH探针和Na-22（+）测量的实验表明，大肠杆菌中表达的五种细菌PP酶具有在生理条件下同时将H+和Na+转运到倒置膜囊泡中的能力。与系统发育分析的数据一致，我们的研究结果支持存在第三个，双特异性细菌Na+，H+-PPase亚家族，这显然是从Na+-PPases进化而来。有趣的是，Na+，H+-PPase的基因已在人类胃肠道的主要微生物中发现。Na+，H+-PP酶需要Na+来进行水解和转运活动，并被K+进一步激活。离子载体效应的基础上，我们得出结论，Na+和H+的运输反应是产电的，并不导致从二次反向效应。序列比较进一步揭示了四个Na+，H+-PPase签名残基位于离子电导通道外的PPases使用X射线晶体学鉴定较早。我们的研究结果共同支持新兴的范式，Na+和H+可以通过相同的机制进行运输，Na+和H+之间的切换特异性只需要在转运蛋白结构的细微变化。
One of the strategies used by organisms to adapt to life under conditions of short energy supply is to use the by-product pyrophosphate to support cation gradients in membranes. Transport reactions are catalyzed by membrane-integral pyrophosphatases (PPases), which are classified into two homologous subfamilies: H+-transporting (found in prokaryotes, protists, and plants) and Na+-transporting (found in prokaryotes). Transport activities have been believed to require specific machinery for each ion, in accordance with the prevailing paradigm in membrane transport. However, experiments using a fluorescent pH probe and Na-22(+) measurements in the current study revealed that five bacterial PPases expressed in Escherichia coli have the ability to simultaneously translocate H+ and Na+ into inverted membrane vesicles under physiological conditions. Consistent with data from phylogenetic analyses, our results support the existence of a third, dual-specificity bacterial Na+, H+-PPase subfamily, which apparently evolved from Na+-PPases. Interestingly, genes for Na+, H+-PPase have been found in the major microbes colonizing the human gastrointestinal tract. The Na+, H+-PPases require Na+ for hydrolytic and transport activities and are further activated by K+. Based on ionophore effects, we conclude that the Na+ and H+ transport reactions are electrogenic and do not result from secondary antiport effects. Sequence comparisons further disclosed four Na+, H+-PPase signature residues located outside the ion conductance channel identified earlier in PPases using X-ray crystallography. Our results collectively support the emerging paradigm that both Na+ and H+ can be transported via the same mechanism, with switching between Na+ and H+ specificities requiring only subtle changes in the transporter structure.