title: Smoke-derived karrikin perception by the α/β-hydrolase KAI2 from Arabidopsis.
abstract: Genetic studies in Arabidopsis implicate an α/β-hydrolase, KARRIKIN-INSENSITIVE 2 (KAI2) as a receptor for karrikins, germination-promoting butenolide small molecules found in the smoke of burned plants. However, direct biochemical evidence for the interaction between KAI2 and karrikin and for the mechanism of downstream signaling by a KAI2-karrikin complex remain elusive. We report crystallographic analyses and ligand-binding experiments for KAI2 recognition of karrikins. The karrikin-1 (KAR1) ligand sits in the opening to the active site abutting a helical domain insert but distal from the canonical catalytic triad (Ser95-His246-Asp217) of α/β-hydrolases, consistent with the lack of detectable hydrolytic activity by purified KAI2. The closest approach of KAR1 to Ser95-His246-Asp217 is 3.8 Å from His246. Six aromatic side chains, including His246, encapsulate KAR1 through geometrically defined aromatic-aromatic interactions. KAR1 binding induces a conformational change in KAI2 at the active site entrance. A crevice of hydrophobic residues linking the polar edge of KAR1 and the helical domain insert suggests that KAI2-KAR1 creates a contiguous interface for binding signaling partners in a ligand-dependent manner.
authors.affiliation: Jack H. Skirball Center for Chemical Biology and Proteomics, Salk Institute for Biological Studies, La Jolla, CA 92037, USA.
authors.forename: Yongxia
authors.initials: Y
authors.lastname: Guo
authors.forename: Zuyu
authors.initials: Z
authors.lastname: Zheng
authors.forename: James J
authors.initials: JJ
authors.lastname: La Clair
authors.forename: Joanne
authors.initials: J
authors.lastname: Chory
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Noel
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000378:metabolism; D005390:Fires; D005663:Furans / Q000378:metabolism*; D006867:Hydrolases / Q000235:genetics / Q000378:metabolism*; D006868:Hydrolysis; D057927:Hydrophobic and Hydrophilic Interactions; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011714:Pyrans / Q000378:metabolism*; D012639:Seeds / Q000378:metabolism; D015398:Signal Transduction; D012906:Smoke
chemical_list: C488803:3-methyl-2H-furo(2,3-c)pyran-2-one; D029681:Arabidopsis Proteins; D005663:Furans; D008024:Ligands; D011714:Pyrans; D012906:Smoke; C558280:HTL protein, Arabidopsis; D006867:Hydrolases
keywords: plant signaling; seed dormancy; wildfires