Brassinosteroid receptor activation
Brassinosteroids are hormones that are important for plant growth, development and immune responses. They are sensed by the transmembrane receptor kinase BRASSINOSTEROID INSENSITIVE 1 (BRI1) when they bind to its extracellular Leu-rich repeat (LRR) domain. Brassinosteroid binding to BRI1 is known to induce conformational changes that create a platform in BRI1 for co-receptor binding. Somatic embryogenesis receptor kinases (SERKs; which are also receptor kinases with LRR ectodomains) have been implicated in mediating brassinosteroid signalling, and their size and membrane localization makes them BRI1 co-receptor candidates. This study reveals that BRI1 and SERK1 interact to activate BRI1 signalling. The authors solved the crystal structure of a ternary complex formed by BRI1, the LRR ectodomain of SERK1 and the hormone at 3.3 Å resolution. Their findings indicate that the SERK1 LRR domain forms an integral part of the ligand-binding pocket of the receptor and thus that BRI1 and SERK1 interact in a ligand-dependent manner. Therefore, the activation of the cytoplasmic kinase domain of BRI1, the underlying mechanism of which was unclear, involves BRI1–SERK1 heterodimerization following extracellular hormone binding at the cell surface.
References
Santiago, J., Henzler, C. & Hothorn, M. Molecular mechanism for plant steroid receptor activation by somatic embryogenesis co-receptor kinases. Science http://dx.doi.org/10.1126/science.1242468 (2013)
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Baumann, K. Structure Watch. Nat Rev Mol Cell Biol 14, 546 (2013). https://doi.org/10.1038/nrm3655
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DOI: https://doi.org/10.1038/nrm3655
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