Interfaculty Institute for Microbiology and Infection Medicine, University of Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany; Department of Protein Evolution, Max Planck Institute for Developmental Biology, Spemannstrasse 35, 72076 Tübingen, Germany.
Lab Adaptation in Microorganisms, Biological Faculty, Saint-Petersburg State University, Universitetskaya em. 7/9, 199034 Saint-Petersburg, Russia.
Cell. 2014 Nov 20;159(5):1188-1199. doi: 10.1016/j.cell.2014.10.015.
Glutamine is the primary metabolite of nitrogen assimilation from inorganic nitrogen sources in microorganisms and plants. The ability to monitor cellular nitrogen status is pivotal for maintaining metabolic homeostasis and sustaining growth. The present study identifies a glutamine-sensing mechanism common in the entire plant kingdom except Brassicaceae. The plastid-localized PII signaling protein controls, in a glutamine-dependent manner, the key enzyme of the ornithine synthesis pathway, N-acetyl-l-glutamate kinase (NAGK), that leads to arginine and polyamine formation. Crystal structures reveal that the plant-specific C-terminal extension of PII, which we term the Q loop, forms a low-affinity glutamine-binding site. Glutamine binding alters PII conformation, promoting interaction and activation of NAGK. The binding motif is highly conserved in plants except Brassicaceae. A functional Q loop restores glutamine sensing in a recombinant Arabidopsis thaliana PII protein, demonstrating the modular concept of the glutamine-sensing mechanism adopted by PII proteins during the evolution of plant chloroplasts.
谷氨酰胺是微生物和植物从无机氮源中吸收氮的主要代谢物。监测细胞氮水平的能力对于维持代谢平衡和促进生长至关重要。本研究鉴定了一种在整个植物界（除十字花科外）普遍存在的谷氨酰胺感应机制。定位于质体的 PII 信号蛋白以依赖于谷氨酰胺的方式控制鸟氨酸合成途径的关键酶，N-乙酰-l-谷氨酰胺激酶（NAGK），从而导致精氨酸和多胺的形成。晶体结构揭示了 PII 的植物特异性 C 端延伸，我们称之为 Q 环，形成了一个低亲和力的谷氨酰胺结合位点。谷氨酰胺结合改变了 PII 的构象，促进了 NAGK 的相互作用和激活。除了十字花科之外，该结合基序在植物中高度保守。功能 Q 环恢复了拟南芥 PII 蛋白中的谷氨酰胺感应，证明了 PII 蛋白在植物叶绿体进化过程中采用的谷氨酰胺感应机制的模块化概念。
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