The, ammonium-inactivated cyanobacterial glutamine synthetase I is reactivated in vivo by a mechanism involving proteolytic removal of its inactivating factors
The, ammonium-inactivated cyanobacterial glutamine synthetase I is reactivated in vivo by a mechanism involving proteolytic removal of its inactivating factors
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DOI：
10.1111/j.1365-2958.2007.05773.x
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发表时间：
2007-07-01
影响因子：
3.6
通讯作者：
Muro-Pastor, M. Isabel
中科院分区：
文献类型：
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作者：
Galmozzi, Carla V.;Fernandez-Avila, M. Jesus;Muro-Pastor, M. Isabel
Synechocystis sp. PCC 6803型谷氨酰胺合成酶I （GS）的活性受两种灭活因子（IF7和IF17）的蛋白-蛋白相互作用过程控制。在添加铵后，编码这些蛋白的基因gifA和gifB分别被下调，导致IF7和IF17的合成，从而使GS失活。除铵后，GS活性在20 min内迅速恢复到初始水平。在这项研究中，我们分析了GS再激活的机制，发现这一过程涉及IF7和IF17的降解。我们发现，铵作为氮源的存在提高了IF17的稳定性，而不是独立于gif基因转录的IF7的稳定性。对聚囊藻粗提物在不同条件下的研究表明，IF7和IF17在体外表现出不同的稳定性。我们发现IF7在体外通过金属蛋白酶的活性降解。此外，通过分析缺乏prp家族基因的聚胞菌突变菌株，体内也证实了可溶性加工多肽酶参与IF7降解。最后，利用一株缺乏GS - 1型的胞囊菌，我们确定了靶蛋白GS对体内IF7和IF17稳定性的关键作用。
The Synechocystis sp. PCC 6803 glutamine synthetase type I (GS) activity is controlled by a process that involves protein-protein interaction with two inactivating factors (IF7 and IF17). Following addition of ammonium, the genes encoding these proteins, gifA and gifB, respectively, are derrepressed, leading to the synthesis of IF7 and IF17 and consequently GS is inactivated. Upon ammonium removal, the GS activity rapidly returns to the initial level within 20 min. In this study, we analyse the mechanism underlying GS reactivation and find that this process involves IF7 and IF17 degradation. We show that the presence of ammonium as nitrogen source enhances IF17 but not IF7 stability independently of gif gene transcription. Studies with Synechocystis crude extracts under different conditions revealed that IF7 and IF17 display different stabilities in vitro. We found that IF7 is degraded in vitro by the activity of metal loproteases. Furthermore, the involvement of soluble processing meta I lopeptidases in IF7 degradation has also been demonstrated in vivo, by analysing Synechocystis mutant strains devoid of genes of the prp family. Finally, using a Synechocystis strain lacking GS type 1, we establish the crucial role of the target protein GS for in vivo IF7 and IF17 stability.