9tp5
Crystal structure of the N-terminal Kelch domain of the Kelch phosphatase BSU1 from Arabidopsis thaliana
Structural highlights
FunctionBSU1_ARATH Phosphatase that acts as a positive regulator of brassinosteroid (BR) signaling (PubMed:14977918, PubMed:21855796). Dephosphorylates BES1, a transcription factor that regulates the expression of BR-response genes, thereby playing an important role in the regulation of response to BRs (PubMed:14977918). Inactivates the negative regulator of BR signaling ASK7/BIN2 by dephosphorylation at 'Tyr-200' (PubMed:21855796).[1] [2] Publication Abstract from PubMedBrassinosteroids (BRs) are plant steroid hormones sensed by the membrane receptor kinase BRI1. Activation of BRI1 leads to the dephosphorylation of BZR1/BES1 transcription factors. Overexpression of the Kelch phosphatase BRI1 SUPPRESSOR 1 (BSU1) rescued the growth defects of bri1 mutants. Subsequent studies identified BSU1 as a protein tyrosine phosphatase, which promotes BR signaling by dephosphorylating a phosphotyrosine in the glycogen synthase kinase 3 BIN2. Crystal structures of the BSU1 phosphatase domain now reveal a high degree of structural similarity to protein phosphatase 1 (PP1), a eukaryotic serine/threonine phosphatase. Consistently, BSU1 efficiently dephosphorylated phosphothreonine- and phosphoserine-containing substrate peptides, but showed no detectable activity toward BIN2 and other phosphotyrosine substrates. A catalytically inactive BSU1 phosphatase domain suppresses the growth phenotypes of the Arabidopsis bri1-5 mutant and binds the BSU1 homologs BSL1-3. bsu1 and bsu1 bsl1 bsl2/3 loss-of-function mutants display wild-type-like BR responses, but exhibit stomatal patterning and fertility defects. Importantly, the PP1-like C-terminal tail of BSU1 is phosphorylated at Thr785 by a cyclin-dependent kinase complex. The phosphorylated tail binds to the BSU1 substrate-binding grooves, blocking access to the active site. Mutation of Thr785 to alanine activates BSU1, suggesting that Kelch phosphatases and PP1 share a common regulatory mechanism. Deletion of the Marchantia polymorpha Kelch phosphatase MpBSLM results in an undifferentiated cell mass phenotype, associated with the overactivation of a cell cycle reporter. Taken together, our experiments suggest that plant Kelch phosphatases act as PP1-like cell cycle regulators, rather than as tyrosine phosphatases in BR signaling. Plant Kelch phosphatases are Ser/Thr phosphatases involved in cell cycle regulation.,Rico-Resendiz F, Pri-Tal O, Raia P, Moretti A, Chen H, Yu J, Broger L, Fuchs C, Hothorn LA, Loubery S, Hothorn M Proc Natl Acad Sci U S A. 2026 May 26;123(21):e2600591123. doi: , 10.1073/pnas.2600591123. Epub 2026 May 20. PMID:42166246[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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