Heterotrimeric GTP-binding protein alpha subunit (Gα) and its cognate regulator of G-protein signaling (RGS) protein transduce signals in eukaryotes spanning protists, amoeba, animals, fungi, and plants. The core catalytic mechanisms of the GTPase activity of Gα and the interaction interface with RGS for the acceleration of GTP hydrolysis seem to be conserved across these groups; however, the gene is under low selective pressure in plants, resulting in its frequent loss. Our current understanding of the structural basis of Gα:RGS regulation in plants has been shaped by Arabidopsis Gα, (AtGPA1), which has a cognate RGS protein. To gain a comprehensive understanding of this regulation beyond Arabidopsis, we obtained the x-ray crystal structures of Gα, which has no RGS, and (a lycophyte) Gα that has low sequence similarity with AtGPA1 but has an RGS. We show that the three-dimensional structure, protein-protein interaction with RGS, and the dynamic features of these Gα are similar to AtGPA1 and metazoan Gα. Molecular dynamic simulation of the Gα-RGS interaction identifies the contacts established by specific residues of the switch regions of GTP-bound Gα, crucial for this interaction, but finds no significant difference due to specific amino acid substitutions. Together, our data provide valuable insights into the regulatory mechanisms of plant G-proteins but do not support the hypothesis of adaptive co-evolution of Gα:RGS proteins in plants.

中文翻译：

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植物 G 蛋白调节机制的结构功能分析确定了关键的 Gα-RGS 蛋白相互作用


异三聚体 GTP 结合蛋白 α 亚基 (Gα) 及其 G 蛋白信号转导 (RGS) 蛋白的同源调节蛋白在真核生物（包括原生生物、阿米巴原虫、动物、真菌和植物）中转导信号。 Gα 的 GTP 酶活性的核心催化机制以及与 RGS 的相互作用界面加速 GTP 水解似乎在这些组中是保守的；然而，该基因在植物中处于低选择压力下，导致其频繁丢失。我们目前对植物中 Gα:RGS 调节的结构基础的理解是由拟南芥 Gα (AtGPA1) 形成的，它具有同源 RGS 蛋白。为了全面了解拟南芥以外的这种调控，我们获得了没有 RGS 的 Gα 和与 AtGPA1 序列相似性较低但有 RGS 的（石松植物）Gα 的 X 射线晶体结构。我们发现这些 Gα 的三维结构、蛋白质与 RGS 的相互作用以及动态特征与 AtGPA1 和后生动物 Gα 相似。 Gα-RGS 相互作用的分子动力学模拟识别了由 GTP 结合的 Gα 开关区域的特定残基建立的接触，这对于这种相互作用至关重要，但没有发现由于特定氨基酸取代而产生的显着差异。总之，我们的数据为植物 G 蛋白的调控机制提供了有价值的见解，但不支持植物中 Gα:RGS 蛋白适应性共同进化的假设。