Journal Article

Structural insight into brassinosteroid perception by BRI1

Yang, Maojun, She, Ji, Wang, Jiawei, Cheng, Wei, Wang, Zhi-Yong, Han, Zhifu, Kim, Tae-Wuk, Shi, Shuai, Wang, Jinjing, Chai, Jijie, Chang, Junbiao

2011

Overview

Brassinosteroids are essential phytohormones that have crucial roles in plant growth and development. Perception of brassinosteroids requires an active complex of BRASSINOSTEROID-INSENSITIVE 1 (BRI1) and BRI1-ASSOCIATED KINASE 1 (BAK1). Recognized by the extracellular leucine-rich repeat (LRR) domain of BRI1, brassinosteroids induce a phosphorylation-mediated cascade to regulate gene expression. Here we present the crystal structures of BRI1(LRR) in free and brassinolide-bound forms. BRI1(LRR) exists as a monomer in crystals and solution independent of brassinolide. It comprises a helical solenoid structure that accommodates a separate insertion domain at its concave surface. Sandwiched between them, brassinolide binds to a hydrophobicity-dominating surface groove on BRI1(LRR). Brassinolide recognition by BRI1(LRR) is through an induced-fit mechanism involving stabilization of two interdomain loops that creates a pronounced non-polar surface groove for the hormone binding. Together, our results define the molecular mechanisms by which BRI1 recognizes brassinosteroids and provide insight into brassinosteroid-induced BRI1 activation. Steroid hormone recognition The brassinolides are potent steroid hormones that are central to plant growth and development. They bind to the plasma membrane receptor BRI1, a member of the leucine-rich repeat (LRR) receptor family that also includes the mammalian Toll-like receptors, which are important in innate immunity. Two independent studies now present the crystal structure of BRI1 from Arabidopsis thaliana , both in the free form and in complex with brassinolide. BRI1 is found to adopt a solenoid-like superhelical structure involving 25 leucine-rich repeats. The structure is strikingly different from that of Toll-like receptors and reveals a novel mechanism of steroid recognition. This work suggests synthetic routes to nonsteroidal mimetics of BRI1 that could have a possible use in agriculture.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 631/449/1741/2670 / 631/45/535 / Agronomy. Soil science and plant productions / Analysis / Arabidopsis / Arabidopsis - chemistry / Arabidopsis - metabolism / Arabidopsis Proteins - chemistry / Arabidopsis Proteins - metabolism / Binding Sites / Biological and medical sciences / Brassinosteroids / Cell receptors / Cholestanols - chemistry / Cholestanols - metabolism / Crystallography, X-Ray / Crystals / Economic plant physiology / Enzyme Activation / Fundamental and applied biological sciences. Psychology / Genetic aspects / Genetics and breeding of economic plants / Growth and development / Growth regulators / Humanities and Social Sciences / Hydrophobic and Hydrophilic Interactions / Kinases / Models, Molecular / multidisciplinary / Phosphorylation / Plant growth / Plant hormones / Protein Binding / Protein Folding / Protein Kinases - chemistry / Protein Kinases - metabolism / Protein Structure, Tertiary / Proteins / Science / Science (multidisciplinary) / Steroids, Heterocyclic - chemistry / Steroids, Heterocyclic - metabolism / Structure / Structure-Activity Relationship / Substrate Specificity