生物谷报道：来自美国华盛顿大学医学院药理学系，印第安纳州大学生物学系，英国剑桥大学化学系的研究人员郑宁获得了拟南芥TIR1–ASK1复合物的晶体结构，从而建立了一种植物激素受体的第一个结构模型，这一研究成果公布在本期（4月5日）《Nature》杂志封面上。
部分英文原文：
Nature 446, 640-645 (5 April 2007) | doi:10.1038/nature05731; Received 27 January 2007; Accepted 8 March 2007
Mechanism of auxin perception by the TIR1 ubiquitin ligase
Xu Tan1, Luz Irina A. Calderon-Villalobos2, Michal Sharon3, Changxue Zheng1, Carol V. Robinson3, Mark Estelle2 & Ning Zheng1
Department of Pharmacology, University of Washington, School of Medicine, Box 357280, Seattle, Washington 98195, USA
Department of Biology, Indiana University, Bloomington, Indiana 47405, USA
Department of Chemistry, University of Cambridge, Cambridge, CB2 1EW, UK
Correspondence to: Ning Zheng1 Correspondence and requests for materials should be addressed to N.Z. (Email: nzheng@u.washington.edu).
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Abstract
Auxin is a pivotal plant hormone that controls many aspects of plant growth and development. Perceived by a small family of F-box proteins including transport inhibitor response 1 (TIR1), auxin regulates gene expression by promoting SCF ubiquitin-ligase-catalysed degradation of the Aux/IAA transcription repressors, but how the TIR1 F-box protein senses and becomes activated by auxin remains unclear. Here we present the crystal structures of the Arabidopsis TIR1–ASK1 complex, free and in complexes with three different auxin compounds and an Aux/IAA substrate peptide. These structures show that the leucine-rich repeat domain of TIR1 contains an unexpected inositol hexakisphosphate co-factor and recognizes auxin and the Aux/IAA polypeptide substrate through a single surface pocket. Anchored to the base of the TIR1 pocket, auxin binds to a partially promiscuous site, which can also accommodate various auxin analogues. Docked on top of auxin, the Aux/IAA substrate peptide occupies the rest of the TIR1 pocket and completely encloses the hormone-binding site. By filling in a hydrophobic cavity at the protein interface, auxin enhances the TIR1–substrate interactions by acting as a 'molecular glue'. Our results establish the first structural model of a plant hormone receptor.
领导这一研究的是来自华盛顿大学的郑宁（Ning Zheng，音译）博士，自2000年以来，郑博士先后在Cell、Nature和Science等国际权威杂志上发表了多篇文章，并且有三篇文章成为杂志的封面故事进行推荐，去年一篇有关泛素蛋白连接酶结构生物学的文章也发表在了10月的《Nature》杂志上。
生长素是最早被发现的一种植物激素。英国的查里·达尔文和他的儿子弗兰西斯·达尔文首先利用金丝雀翳（yi）草胚芽鞘进行向光性实验，发现在单方向光照射下，胚芽鞘向光弯曲；如果切去胚芽鞘的尖端或在尖端套上锡箔小帽，单侧光照也不会使胚芽鞘向光弯曲；如果单侧光不照射胚芽鞘尖端而只向下照射胚芽鞘下部，胚芽鞘还是会向光弯曲。当时，他们推测：胚芽鞘向光弯曲是由于幼苗在单侧光照射下，产生某种影响，从上部传到下部，造成背光的一侧生长快，而这种“影响”就是植物生长素Auxin。
之后的研究证明生长素Auxin是一种关键的植物激素，能调控植物生长和发育的许多方面，在对一个小家族：F-box蛋白（包括转运抑制应答因子1（transport inhibitor response 1，TIR1）的研究中发现，生长素Auxin可以通过促进SCF对Aux/IAA转录抑制子的泛素连接酶（ubiquitin-ligase）催化降解，来调控基因的表达，但是TIR1 F-box蛋白是如何感应，以及通过生长素Auxin激活仍然是这一领域的一个未知之谜。
