title: Structure and binding specificity of the receiver domain of sensor histidine kinase CKI1 from Arabidopsis thaliana.
abstract: Multistep phosphorelay (MSP) signaling mediates responses to a variety of important stimuli in plants. In Arabidopsis MSP, the signal is transferred from sensor histidine kinase (HK) via histidine phosphotransfer proteins (AHP1-AHP5) to nuclear response regulators. In contrast to ancestral two-component signaling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. Here, we show that the C-terminal receiver domain of HK CKI1 (CKI1(RD) ) is responsible for the recognition of CKI1 downstream signaling partners, and specifically interacts with AHP2, AHP3 and AHP5 with different affinities. We studied the effects of Mg²⁺, the co-factor necessary for signal transduction via MSP, and phosphorylation-mimicking BeF₃⁻ on CKI1(RD) in solution, and determined the crystal structure of free CKI1(RD) and CKI1(RD) in a complex with Mg²⁺. We found that the structure of CKI1(RD) shares similarities with the only known structure of plant HK, ETR1(RD) , with the main differences being in loop L3. Magnesium binding induces the rearrangement of some residues around the active site of CKI1(RD) , as was determined by both X-ray crystallography and NMR spectroscopy. Collectively, these results provide initial insights into the nature of molecular mechanisms determining the specificity of MSP signaling and MSP catalysis in plants.
authors.affiliation: Department of Functional Genomics and Proteomics, Masaryk University, Kotlářská 2, CZ-61137 Brno, Czech Republic.
authors.forename: Blanka
authors.initials: B
authors.lastname: Pekárová
authors.forename: Tomáš
authors.initials: T
authors.lastname: Klumpler
authors.forename: Olga
authors.initials: O
authors.lastname: Třísková
authors.forename: Jakub
authors.initials: J
authors.lastname: Horák
authors.forename: Séverine
authors.initials: S
authors.lastname: Jansen
authors.forename: Radka
authors.initials: R
authors.lastname: Dopitová
authors.forename: Petra
authors.initials: P
authors.lastname: Borkovcová
authors.forename: Veronika
authors.initials: V
authors.lastname: Papoušková
authors.forename: Eliška
authors.initials: E
authors.lastname: Nejedlá
authors.forename: Vladimír
authors.initials: V
authors.lastname: Sklenář
authors.forename: Jaromír
authors.initials: J
authors.lastname: Marek
authors.forename: Lukáš
authors.initials: L
authors.lastname: Zídek
authors.forename: Jan
authors.initials: J
authors.lastname: Hejátko
authors.forename: Lubomír
authors.initials: L
authors.lastname: Janda
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000502:physiology; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D018360:Crystallography, X-Ray; D006639:Histidine / Q000378:metabolism; D008958:Models, Molecular; D009154:Mutation; D010766:Phosphorylation; D010770:Phosphotransferases / Q000235:genetics / Q000378:metabolism*; D025941:Protein Interaction Mapping; D011494:Protein Kinases / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins; D012680:Sensitivity and Specificity; D015398:Signal Transduction / Q000502:physiology
chemical_list: D029681:Arabidopsis Proteins; D011993:Recombinant Fusion Proteins; D006639:Histidine; D010770:Phosphotransferases; D011494:Protein Kinases; C101990:CKI1 protein, Arabidopsis