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Crystal structures of the phosphorylated BRI1 kinase domain and implications for brassinosteroid signal initiation

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journal contribution
posted on 22.02.2016, 14:43 by D. Bojar, J. Martinez, J. Santiago, V. Rybin, Richard Bayliss, M. Hothorn
Brassinosteroids, which control plant growth and development, are sensed by the membrane receptor kinase BRASSINOSTEROID INSENSITIVE 1 (BRI1). Brassinosteroid binding to the BRI1 leucine-rich repeat (LRR) domain induces heteromerisation with a SOMATIC EMBRYOGENESIS RECEPTOR KINASE (SERK)-family co-receptor. This process allows the cytoplasmic kinase domains of BRI1 and SERK to interact, trans-phosphorylate and activate each other. Here we report crystal structures of the BRI1 kinase domain in its activated form and in complex with nucleotides. BRI1 has structural features reminiscent of both serine/threonine and tyrosine kinases, providing insight into the evolution of dual-specificity kinases in plants. Phosphorylation of Thr1039, Ser1042 and Ser1044 causes formation of a catalytically competent activation loop. Mapping previously identified serine/threonine and tyrosine phosphorylation sites onto the structure, we analyse their contribution to brassinosteroid signaling. The location of known genetic missense alleles provide detailed insight into the BRI1 kinase mechanism, while our analyses are inconsistent with a previously reported guanylate cyclase activity. We identify a protein interaction surface on the C-terminal lobe of the kinase and demonstrate that the isolated BRI1, SERK2 and SERK3 cytoplasmic segments form homodimers in solution and have a weak tendency to heteromerise. We propose a model in which heterodimerisation of the BRI1 and SERK ectodomains brings their cytoplasmic kinase domains in a catalytically competent arrangement, an interaction that can be modulated by the BRI1 inhibitor protein BKI1.

Funding

This work was supported by the Max Planck Society, by a Federation of European Biochemical Societies long-term fellowship (J.S.), by a Royal Society Research Fellowship (R.B.) and by an International Human Frontier Science Program Organisation Career Development Award (M.H.). D.B. is a fellow of the German National Academic Foundation.

History

Citation

The Plant Journal (2014) 78, 31–43

Version

VoR (Version of Record)

Published in

The Plant Journal (2014) 78

Publisher

Wiley, Society for Experimental Biology (SEB)

issn

0960-7412

eissn

1365-313X

Acceptance date

16/01/2014

Copyright date

2014

Available date

22/02/2016

Publisher version

http://onlinelibrary.wiley.com/doi/10.1111/tpj.12445/abstract

Notes

Atomic coordinates and structure factors have been deposited with the Protein Data Bank with accession codes 4OA2 (BRI1865–1196 ADP), 4OA6 (BRI1865–1160 apo), 4OA9 (BRI1865–1160 Mn2+/AppNHp), 4OAB (BRI1865–1160 ATP) and 4OAC (BRI1865–1160 ADP).

Language

en