清华大学兼职教授颜宁博士以及王佳伟副研究员领导的研究组于11月5日在Nature Structural & Molecular Biology上发表学术论文“Structural Insights into the mechanism of Abscisic acid signaling by PYL proteins”，系统阐述了脱落酸受体介导脱落酸信号传导的分子机制。
脱落酸（Abscisic acid, ABA）是植物中最为重要的激素之一，它与种子休眠、根系发育、叶子枯萎、抗旱反应和其它的生理过程都有极为密切的关系。由于脱落酸能引发的下游反应过多，包括激酶、磷酸酶、G蛋白、泛素通路中的蛋白等等都参与了ABA信号的调控，因此从ABA被发现半个世纪以来一直不清楚ABA的受体是什么。过去几年陆续有一些关于ABA受体的发现报导，但其具体功能尚有所争议。今年四月底，Science发表两个独立研究组的最新成果，发现一类被命名为PYR/PYL或是RCAR的蛋白为ABA受体。这类蛋白可以在体内外结合ABA，之后会结合下游的蛋白磷酸酶PP2C并抑制其磷酸酶活性，然而其中的分子机制尚不清楚。并且由于之前关于ABA受体的诸多争议，PYL蛋白是否为真正的ABA受体也还有待进一步验证。在这种背景下，结构生物学研究变得至关重要。
颜宁教授的研究组自2007年建立之初就开始了对于ABA受体的结构生物学研究。此次，在医学院颜宁教授和生命学院王佳伟博士的指导下，由生命学院和医学院的博士后及研究生联手历时四个月完成的研究成果报道了PYL蛋白在1）没有ABA，2）结合ABA，以及3）同时结合ABA和下游PP2C的三个状态下的高分辨率分子结构。通过结构比较和生化分析，确认PYL蛋白为ABA受体，并且发现其中一个被命名为CL2的蛋白柔性区在介导ABA信号及抑制PP2C活性中起了至关重要的作用。（生物谷Bioon.com）
生物谷推荐原始出处：
Nature Structural & Molecular Biology 5 November 2009 | doi:10.1038/nsmb.1730
Structural insights into the mechanism of abscisic acid signaling by PYL proteins
Ping Yin1,2,4, He Fan1,2,4, Qi Hao1,3,4, Xiaoqiu Yuan1,3,4, Di Wu1,2, Yuxuan Pang1,2, Chuangye Yan1,2, Wenqi Li1,3, Jiawei Wang1,2 & Nieng Yan1,3
Abstract
Abscisic acid (ABA) is an important phytohormone that regulates plant stress responses. Proteins from the PYR-PYL-RCAR family were recently identified as ABA receptors. Upon binding to ABA, a PYL protein associates with type 2C protein phosphatases (PP2Cs) such as ABI1 and ABI2, inhibiting their activity; the molecular mechanisms by which PYLs mediate ABA signaling remain unknown, however. Here we report three crystal structures: apo-PYL2, (+)-ABA-bound PYL2 and (+)-ABA-bound PYL1 in complex with phosphatase ABI1. Apo-PYL2 contains a pocket surrounded by four highly conserved surface loops. In response to ABA binding, loop CL2 closes onto the pocket, creating a surface that recognizes ABI1. In the ternary complex, the CL2 loop is located near the active site of ABI1, blocking the entry of substrate proteins. Together, our data reveal the mechanisms by which ABA regulates PYL-mediated inhibition of PP2Cs.
1 State Key Laboratory of Bio-membrane and Membrane Biotechnology
2 Center for Structural Biology, School of Life Sciences
3 School of Medicine, Tsinghua University, Beijing, China.
4 These authors contributed equally to this work.
