Abstract
Plant-unique receptor kinases harbor conserved cytoplasmic kinase domains and sequence-diverse ectodomains. Here we report crystal structures of CRINKLY4-type ectodomains from Arabidopsis ACR4 and Physcomitrella patens PpCR4 at 1.95 Å and 2.70 Å resolution, respectively. Monomeric CRINKLY4 ectodomains harbor a N-terminal WD40 domain and a cysteine-rich domain (CRD) connected by a short linker. The WD40 domain forms a seven-bladed β-propeller with the N-terminal strand buried in its center. Each propeller blade is stabilized by a disulfide bond. The CRD forms a β-sandwich structure stabilized by six disulfide bonds and shares low structural homology with tumor necrosis factor receptor domains. Quantitative binding assays reveal that ACR4 is not a direct receptor for the peptide hormone CLE40. An ACR4 variant lacking the entire CRD can rescue the known acr4-2 mutant phenotype, as can expression of PpCR4. Together, an evolutionary conserved signaling function for CRINKLY4 receptor kinases is encoded in its WD40 domain.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
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