EMBL Hamburg Outstation, Hamburg, Germany.
J Mol Biol. 2012 Jan 27;415(4):768-79. doi: 10.1016/j.jmb.2011.11.046. Epub 2011 Dec 7.
Ethylene controls many aspects of plant growth and development. Signaling by the gaseous phytohormone is initiated by disulfide-linked membrane-bound receptors, and the formation of heteromeric receptor clusters contributes to the broad range of ethylene responsiveness. In Arabidopsis thaliana, the TCS-like ethylene receptors interact with the cytosolic serine/threonine kinase constitutive triple response 1 (CTR1), a proposed mitogen-activated protein kinase kinase kinase. In the absence of the hormone, the receptor and therefore CTR1 are active. Hence, ethylene acts as an inverse agonist of its signaling pathway. The three-dimensional structures of the active, triphosphorylated and the unphosphorylated, inactive kinase domain of CTR1 in complex with staurosporine illustrate the conformational rearrangements that form the basis of activity regulation. Additionally, in analytical ultracentrifugation experiments, active kinase domains form back-to-back dimers, while inactive and activation loop variants are monomers. Together with a front-to-front activation interface, the active protein kinase dimers thereby engage in interactions that promote CTR1-mediated cross talk between ethylene receptor clusters. This model provides a structural foundation for the observed high sensitivity of plants to ethylene.
乙烯控制着植物生长和发育的许多方面。这种气态植物激素的信号传递是由二硫键连接的膜结合受体启动的，而异源受体簇的形成有助于广泛的乙烯反应。在拟南芥中，TCS 样乙烯受体与胞质丝氨酸/苏氨酸激酶组成型三重反应 1（CTR1）相互作用，CTR1 被认为是一种丝裂原激活蛋白激酶激酶激酶。在没有激素的情况下，受体因此也是活跃的。因此，乙烯是其信号通路的反向激动剂。CTR1 的活性、三磷酸化和非磷酸化的、无活性激酶结构域与星孢菌素复合物的三维结构说明了形成活性调节基础的构象重排。此外，在分析超速离心实验中，活性激酶结构域形成背对背二聚体，而无活性和激活环变体是单体。与正面到正面的激活界面一起，活性蛋白激酶二聚体因此参与促进乙烯受体簇之间的 CTR1 介导的串扰的相互作用。该模型为植物对乙烯的高敏感性提供了结构基础。
