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首页> 外文期刊>Biochemistry >A Source of Ultrasensitivity in the Glutamine Response of the Bicyclic Cascade System Controlling Glutamine Synthetase Adenylylation State and Activity in Escherichia coli
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A Source of Ultrasensitivity in the Glutamine Response of the Bicyclic Cascade System Controlling Glutamine Synthetase Adenylylation State and Activity in Escherichia coli

机译：控制谷氨酰胺合成酶腺苷酸化状态和活性的双环级联系统的谷氨酰胺响应中的超敏性来源。

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摘要

Glutamine synthetase (GS) activity in Escherichia coli is regulated by reversible adenylylation, brought about by a bicyclic system comprised of uridylyltransferase/ uridylyl-removing enzyme (UTase/UR), its substrate, PII, adenylyltransferase (ATase), and its substrate, GS. The modified and unmodified forms of PII produced by the upstream UTase/UR-PII cycle regulate the downstream ATase-GS cycle. A reconstituted UTase/UR-PII-ATase-GS bicyclic system has been shown to produce a highly ultrasensitive response of GS adenylylation state to the glutamine concentration, but its composite UTase/UR-PII and ATase-GS cycles displayed moderate glutamine sensitivities when examined separately. Glutamine sensitivity of the bicyclic system was significantly reduced when the trimeric PII protein was replaced by a heterotrimeric form of PII that was functionally monomeric, and coupling between the two cycles was different in systems containing wild-type or heterotrimeric PII. Thus, the trimeric nature of PII played a role in the glutamine response of the bicyclic system. We therefore examined regulation of the individual AT (adenylylation) and AR (deadenylylation) activities of ATase by PII preparations with various levels of uridylylation. AR activity was affected in a linear fashion by PII uridylylation, but partially modified wild-type PII activated the AT much less than expected based on the extent of PII modification. Partially modified wild-type PII also bound to ATase less than expected based upon the fraction of modified subunits. Our results suggest that the AT activity is only bound and activated by completely unmodified PII and that this design is largely responsible for ultrasensitivity of the bicyclic system.
机译：大肠杆菌中的谷氨酰胺合成酶（GS）活性受可逆的腺苷酸化作用调控，该过程由双环系统实现，该系统由尿酸转移酶/尿酸去除酶（UTase / UR），其底物PII，腺苷酸转移酶（ATase）以及其底物GS组成。上游UTase / UR-PII循环产生的PII修饰形式和未修饰形式调节下游ATase-GS循环。已显示重构的UTase / UR-PII-ATase-GS双环系统可产生GS腺苷酸化状态对谷氨酰胺浓度的高度超灵敏响应，但当检查时，其复合UTase / UR-PII和ATase-GS循环显示中等的谷氨酰胺敏感性分别。当三聚体PII蛋白被功能性单体的PII异源三聚体形式取代时，双环系统的谷氨酰胺敏感性显着降低，并且在包含野生型或异源三聚体PII的系统中，两个循环之间的偶联不同。因此，PII的三聚体性质在双环系统的谷氨酰胺响应中起作用。因此，我们研究了通过尿嘧啶水平不同的PII制剂对ATase的单个AT（腺苷酰化）和AR（脱腺苷酸化）活性的调节。 AR活性受到PII尿酰化作用的线性影响，但部分修饰的野生型PII激活AT的能力远低于基于PII修饰程度的预期。基于修饰的亚基的比例，部分修饰的野生型PII与ATase的结合也少于预期。我们的结果表明，AT活性仅由完全未修饰的PII结合和激活，并且这种设计在很大程度上负责了双环系统的超敏感性。

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