Anion-exchange mechanisms in bacteria.
Anion-exchange mechanisms in bacteria.
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细菌中的阴离子交换机制。
DOI：
10.1128/mr.54.1.1-17.1990
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发表时间：
1990
期刊：
影响因子：
--
通讯作者：
Varadhachary,A
中科院分区：
文献类型：
--
作者：
Maloney,PC;Ambudkar,SV;Anatharam,V;Sonna,LA;Varadhachary,A
本文讨论了细菌阴离子交换反应的生理，生化和分子特性，特别关注磷酸盐（Pi）连接的反向转运蛋白家族，其接受糖磷酸盐作为其主要底物，如葡萄糖6-磷酸（G6 P），甘露糖6-磷酸或甘油3-磷酸。Pi连锁的反向转运蛋白可以在革兰氏阳性和革兰氏阴性细胞中发现。正如它们的名字所暗示的，这些交换蛋白接受无机和有机磷酸盐，但这两类底物与蛋白质的相互作用非常不同。因此，Pi总是以相对较低的亲和力被接受，并且当它参与交换时，它总是被视为单价阴离子。相比之下，当使用高亲和力有机磷酸盐时，这些相同的系统无法区分一价和二价形式。异源交换试验（例如，圆周率：G6 P）表明这些蛋白质具有双功能活性位点，其接受一对负电荷，无论是作为两个单价阴离子还是作为单个二价阴离子。出于这个原因，交换化学计量在2：1和2：2的极限之间移动，根据在任一膜表面的一价和二价底物的比率。由于G6 P具有在生理范围内的pK 2（pK为6.1），这预测了一种新的体内反应序列，因为内部pH比外部pH更碱性。因此，人们预期作为两个单价G6 P阴离子的不对称交换从相对酸性的外部移动对单个二价G6 P从碱性内部。以这种方式，G6 P的无效自我交换可以偏向于由pH梯度（间接）驱动的净向内通量。尽管Pi连接的反向转运蛋白表现出生物化学复杂性，但它们在分子水平上类似于所有其他二级载体，并显示出可能的拓扑结构，其中两组六个跨膜α-螺旋通过中心亲水环连接。对这种常见形式的推导的推测表明，容纳这种蛋白质的结构模型数量有限。三个这样的模型。
This article discusses the physiological, biochemical, and molecular properties of bacterial anion-exchange reactions, with a particular focus on a family of phosphate (Pi)-linked antiporters that accept as their primary substrates sugar phosphates such as glucose 6-phosphate (G6P), mannose 6-phosphate, or glycerol 3-phosphate. Pi-linked antiporters may be found in both gram-positive and gram-negative cells. As their name suggests, these exchange proteins accept both inorganic and organic phosphates, but the two classes of substrate interact very differently with the protein. Thus, Pi is always accepted with a relatively low affinity, and when it participates in exchange, it is always taken as the monovalent anion. By contrast, when the high-affinity organic phosphates are used, these same systems fail to discriminate between monovalent and divalent forms. Tests of heterologous exchange (e.g., Pi: G6P) indicate that these proteins have a bifunctional active site that accepts a pair of negative charges, whether as two monovalent anions or as a single divalent anion. For this reason, exchange stoichiometry moves between limits of 2:1 and 2:2, according to the ratio of mono- and divalent substrates at either membrane surface. Since G6P has a pK2 within the physiological range (pK of 6.1), this predicts a novel reaction sequence in vivo because internal pH is more alkaline than external pH. Accordingly, one expects an asymmetric exchange as two monovalent G6P anions from the relatively acidic exterior move against a single divalent G6P from the alkaline interior. In this way an otherwise futile self-exchange of G6P can be biased towards a net inward flux driven (indirectly) by the pH gradient. Despite the biochemical complexity exhibited by Pi-linked antiporters, they resemble all other secondary carriers at a molecular level and show a likely topology in which two sets of six transmembrane alpha-helices are connected by a central hydrophilic loop. Speculations on the derivation of this common form suggest a limited number of structural models to accommodate such proteins. Three such models are presented.
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