Pekarova B, Klumpler T, Triskova O, Horak J, Jansen S, Dopitova R, Papouskova V, Nejedla E, Sklenar V, Marek J, Zidek L, Hejatko J, Janda L

Multistep phosphorelay (MSP) signaling mediates response to a variety of important stimuli in plants. In Arabidopsis MSP, the signal is transferred from sensor histidine kinase (HK) via histidine phosphotransfer proteins (AHP1-5) to nuclear response regulators. In contrast to ancestral two-component signaling in bacteria, protein interactions in plant MSP are supposed ...

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to be rather nonspecific. Here, we show that the C-terminal receiver domain of HK CKI1 (CKI1(RD) ) is responsible for recognition of CKI1 downstream signaling partners and specifically interacts with AHP2, AHP3, and AHP5 with different affinities. We studied the effects of Mg(2+) , the cofactor necessary for signal transduction via MSP, and phosphorylation-mimicking BeF(3) (-) on CKI1(RD) in solution and we determined the crystal structure of free CKI1(RD) and CKI1(RD) in a complex with Mg(2+) . We found that CKI1(RD) structure shares similarities with the only known structure of plant HK, ETR1(RD) , with the main differences being in loop L3. Magnesium binding induces 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 specificity of MSP signaling and MSP catalysis in plants.

Date: May. 13, 2011

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