title: Specific binding of gibberellic acid by cytokinin-specific binding proteins: a new aspect of plant hormone-binding proteins with the PR-10 fold.
abstract: Pathogenesis-related proteins of class 10 (PR-10) are a family of plant proteins with the same fold characterized by a large hydrophobic cavity that allows them to bind various ligands, such as phytohormones. A subfamily with only ~20% sequence identity but with a conserved canonical PR-10 fold have previously been recognized as Cytokinin-Specific Binding Proteins (CSBPs), although structurally the binding mode of trans-zeatin (a cytokinin phytohormone) was found to be quite diversified. Here, it is shown that two CSBP orthologues from Medicago truncatula and Vigna radiata bind gibberellic acid (GA3), which is an entirely different phytohormone, in a conserved and highly specific manner. In both cases a single GA3 molecule is found in the internal cavity of the protein. The structural data derived from high-resolution crystal structures are corroborated by isothermal titration calorimetry (ITC), which reveals a much stronger interaction with GA3 than with trans-zeatin and pH dependence of the binding profile. As a conclusion, it is postulated that the CSBP subfamily of plant PR-10 proteins should be more properly linked with general phytohormone-binding properties and termed phytohormone-binding proteins (PhBP).
authors.affiliation: Center for Biocrystallographic Research, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan, Poland.
authors.forename: Milosz
authors.initials: M
authors.lastname: Ruszkowski
authors.affiliation: Center for Biocrystallographic Research, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan, Poland.
authors.forename: Joanna
authors.initials: J
authors.lastname: Sliwiak
authors.affiliation: Center for Biocrystallographic Research, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan, Poland.
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Ciesielska
authors.affiliation: Center for Biocrystallographic Research, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan, Poland.
authors.forename: Jakub
authors.initials: J
authors.lastname: Barciszewski
authors.affiliation: Center for Biocrystallographic Research, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan, Poland.
authors.forename: Michal
authors.initials: M
authors.lastname: Sikorski
authors.affiliation: Center for Biocrystallographic Research, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan, Poland.
authors.forename: Mariusz
authors.initials: M
authors.lastname: Jaskolski
mesh_terms: D002151:Calorimetry; D003583:Cytokinins / Q000378:metabolism*; D005875:Gibberellins / Q000378:metabolism*; D010937:Plant Growth Regulators / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism*; D011485:Protein Binding
chemical_list: D003583:Cytokinins; D005875:Gibberellins; D010937:Plant Growth Regulators; D010940:Plant Proteins; C007842:gibberellic acid
keywords: Cytokinin-Specific Binding Proteins; gibberellic acid; pathogenesis-related proteins of class 10; phytohormone-binding proteins