Ammonium sensing in Escherichia coli -: Role of the ammonium transporter AmtB and AmtB-GlnK complex formation
Ammonium sensing in Escherichia coli -: Role of the ammonium transporter AmtB and AmtB-GlnK complex formation
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DOI：
10.1074/jbc.m312399200
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发表时间：
2004-03-05
影响因子：
4.8
通讯作者：
Merrick, M
中科院分区：
文献类型：
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作者：
Javelle, A;Severi, E;Merrick, M
铵转运蛋白是高亲和力的铵转运蛋白，在生命的所有领域都是保守的。在细菌和古细菌中，染色体结构基因（amtB）总是与glnK相连，glnK编码P-II信号转导蛋白家族的一员，该蛋白调节氮代谢的许多方面。我们现在已经表明，大肠杆菌AmtB是通过与GlnK形成膜结合复合物而失活的。复合物的形成是可逆的，并在几秒钟内发生在响应于细胞外铵浓度的微摩尔变化。调节由GlnK的尿苷酰化/去尿苷酰化介导，直接响应细胞内谷氨酰胺库的波动。此外，在生理条件下，GlnK脱氧尿苷酰化需要AmtB活性。因此，转运蛋白是信号转导级联的一个组成部分，AmtB可以被正式视为铵传感器。该系统提供了一种非常敏感的机制来控制铵通量进入细胞，并且glnK与amtB的连接的保守性表明这种调节机制可能发生在整个原核生物中。
The Amt proteins are high affinity ammonium transporters that are conserved in all domains of life. In bacteria and archaea the Amt structural genes ( amtB) are invariably linked to glnK, which encodes a member of the P-II signal transduction protein family, proteins that regulate many facets of nitrogen metabolism. We have now shown that Escherichia coli AmtB is inactivated by formation of a membrane-bound complex with GlnK. Complex formation is reversible and occurs within seconds in response to micromolar changes in the extracellular ammonium concentration. Regulation is mediated by the uridylylation/deuridylylation of GlnK in direct response to fluctuations in the intracellular glutamine pool. Furthermore under physiological conditions AmtB activity is required for GlnK deuridylylation. Hence the transporter is an integral part of the signal transduction cascade, and AmtB can be formally considered to act as an ammonium sensor. This system provides an exquisitely sensitive mechanism to control ammonium flux into the cell, and the conservation of glnK linkage to amtB suggests that this regulatory mechanism may occur throughout prokaryotes.