5n2n | pdb_00005n2n
Crystal structure of the receiver domain of the histidine kinase CKI1 from Arabidopsis thaliana complexed with Mg2+ and BeF3-
Structural highlights
FunctionCKI1_ARATH Essential protein. Functions as a histidine kinase and transmits the stress signal to a downstream MAPK cascade. This protein undergoes an ATP-dependent autophosphorylation at a conserved histidine residue in the kinase core, and a phosphoryl group is then transferred to a conserved aspartate residue in the receiver domain. Required for the development of megagametophyte in female gametophyte (embryo sac) independently of cytokinin. Contributes to vascular bundle formation and secondary growth in a cytokinin-independent manner, probably by promoting the maintenance of mitotic activity and/or identity of procambial cells. Seems to influence and promote the cytokinin signaling pathway.[1] [2] [3] [4] [5] [6] [7] Publication Abstract from PubMedMultistep phosphorelay (MSP) cascades mediate responses to a wide spectrum of stimuli, including plant hormonal signaling, but several aspects of MSP await elucidation. Here, we provide first insight into the key step of MSP-mediated phosphotransfer in a eukaryotic system, the phosphorylation of the receiver domain of the histidine kinase CYTOKININ INDEPENDENT 1 (CKI1RD) from Arabidopsis thaliana We observed that the crystal structures of free, Mg2+-bound, and beryllofluoridated CKI1RD (a stable analog of the labile phosphorylated form) were identical and similar to the active state of receiver domains of bacterial response regulators. However, the three CKI1RD variants exhibited different conformational dynamics in solution. NMR studies revealed that Mg2+ binding and beryllofluoridation alter the conformational equilibrium of the beta3-alpha3 loop close to the phosphorylation site. Mutations that perturbed the conformational behavior of the beta3-alpha3 loop while keeping the active site aspartate intact resulted in suppression of CKI1 function. Mechanistically, homology modeling indicated that the beta3-alpha3 loop directly interacts with the ATP-binding site of the CKI1 histidine kinase domain. The functional relevance of the conformational dynamics observed in the beta3-alpha3 loop of CKI1RD was supported by a comparison with another A. thaliana histidine kinase, ETR1. In contrast to the highly dynamic beta3-alpha3 loop of CKI1RD, the corresponding loop of the ETR1 receiver domain (ETR1RD) exhibited little conformational exchange and adopted a different orientation in crystals. Biochemical data indicated that ETR1RD is involved in phosphorylation-independent signaling, implying a direct link between conformational behavior and the ability of eukaryotic receiver domains to participate in MSP. Conformational dynamics as a key factor of signaling mediated by the receiver domain of sensor histidine kinase from Arabidopsis thaliana.,Otrusinova O, Demo G, Padrta P, Jasenakova Z, Pekarova B, Gelova Z, Szmitkowska A, Kaderavek P, Jansen S, Zachrdla M, Klumpler T, Marek J, Hritz J, Janda L, Iwai H, Wimmerova M, Hejatko J, Zidek L J Biol Chem. 2017 Aug 31. pii: jbc.M117.790212. doi: 10.1074/jbc.M117.790212. PMID:28860196[8] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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