The structures of cytosolic and plastid-located glutamine synthetases from Medicago truncatula reveal a common and dynamic architecture.
The structures of cytosolic and plastid-located glutamine synthetases from Medicago truncatula reveal a common and dynamic architecture.
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DOI：
10.1107/s1399004713034718
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发表时间：
2014-04
期刊：
影响因子：
--
通讯作者：
Pereira PJ
中科院分区：
文献类型：
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作者：
Torreira E;Seabra AR;Marriott H;Zhou M;Llorca Ó;Robinson CV;Carvalho HG;Fernández-Tornero C;Pereira PJ
双子叶细胞质和质体定位的谷氨酰胺合成酶的实验模型揭示了保守的真核型十聚体结构，蒺藜麦同工酶具有微妙的结构差异，这解释了它们独特的除草剂抗性。高等植物氮同化的第一步，即能量驱动的氨与谷氨酸的结合，是由谷氨酰胺合成酶催化的。这一核心过程产生易于代谢的谷氨酰胺，而谷氨酰胺又是所有后续含氮化合物生物合成的基础。谷氨酰胺合成酶的重要作用使其成为除草化合物的主要靶标，同时也是提高作物产量的合适干预点。尽管大多数农作物是双子叶植物，但人们对这些生物体中谷氨酰胺合成酶的结构组织以及不同异构体之间的功能差异知之甚少。在此，报告了来自模型豆科植物蒺藜苜蓿的两种谷氨酰胺合成酶亚型的结构特征：细胞质 GSII-1a 的晶体结构和位于质体的 GSII-2a 的电子冷冻显微镜重建。这些结构模型共同揭示了双子叶谷氨酰胺合成酶的十聚体组织，其中两个五聚环通过环间环弱连接。此外，这些动态环的重新排列改变了环的相对方向，表明它们组装成十聚体酶的类似拉链的机制。最后，M. truncatula GSII-1a 的原子结构为该酶家族除草剂抗性的结构决定因素提供了重要见解，为开发抗除草剂植物开辟了新途径。
The experimental models of dicotyledonous cytoplasmic and plastid-located glutamine synthetases unveil a conserved eukaryotic-type decameric architecture, with subtle structural differences in M. truncatula isoenzymes that account for their distinct herbicide resistance. The first step of nitrogen assimilation in higher plants, the energy-driven incorporation of ammonia into glutamate, is catalyzed by glutamine synthetase. This central process yields the readily metabolizable glutamine, which in turn is at the basis of all subsequent biosynthesis of nitrogenous compounds. The essential role performed by glutamine synthetase makes it a prime target for herbicidal compounds, but also a suitable intervention point for the improvement of crop yields. Although the majority of crop plants are dicotyledonous, little is known about the structural organization of glutamine synthetase in these organisms and about the functional differences between the different isoforms. Here, the structural characterization of two glutamine synthetase isoforms from the model legume Medicago truncatula is reported: the crystallographic structure of cytoplasmic GSII-1a and an electron cryomicroscopy reconstruction of plastid-located GSII-2a. Together, these structural models unveil a decameric organization of dicotyledonous glutamine synthetase, with two pentameric rings weakly connected by inter-ring loops. Moreover, rearrangement of these dynamic loops changes the relative orientation of the rings, suggesting a zipper-like mechanism for their assembly into a decameric enzyme. Finally, the atomic structure of M. truncatula GSII-1a provides important insights into the structural determinants of herbicide resistance in this family of enzymes, opening new avenues for the development of herbicide-resistant plants.