PMID:22090030

Citation	Xie, T, Ren, R, Zhang, YY, Pang, Y, Yan, C, Gong, X, He, Y, Li, W, Miao, D, Hao, Q, Deng, H, Wang, Z, Wu, JW and Yan, N (2012) Molecular mechanism for inhibition of a critical component in the Arabidopsis thaliana abscisic acid signal transduction pathways, SnRK2.6, by protein phosphatase ABI1. J. Biol. Chem. 287:794-802
Abstract	Subclass III SnRK2s (SnRK2.6/2.3/2.2) are the key positive regulators of abscisic acid (ABA) signal transduction in Arabidopsis thaliana. The kinases, activated by ABA or osmotic stress, phosphorylate stress-related transcription factors and ion channels, which ultimately leads to the protection of plants from dehydration or high salinity. In the absence of stressors, SnRK2s are subject to negative regulation by group A protein phosphatase type 2Cs (PP2C), whereas the underlying molecular mechanism remains to be elucidated. Here we report the crystal structure of the kinase domain of SnRK2.6 at 2.6-Å resolution. Structure-guided biochemical analyses identified two distinct interfaces between SnRK2.6 and ABI1, a member of group A PP2Cs. Structural modeling suggested that the two interfaces lock SnRK2.6 and ABI1 in an orientation such that the activation loop of SnRK2.6 is posited to the catalytic site of ABI1 for dephosphorylation. These studies revealed the molecular basis for PP2Cs-mediated inhibition of SnRK2s and provided important insights into the downstream signal transduction of ABA.
Links	PubMed PMC3249133 Online version:10.1074/jbc.M111.313106
Keywords	Abscisic Acid/metabolism; Amino Acid Sequence; Arabidopsis/cytology; Arabidopsis/enzymology; Arabidopsis/metabolism; Arabidopsis Proteins/chemistry; Arabidopsis Proteins/genetics; Arabidopsis Proteins/metabolism; Crystallography, X-Ray; Enzyme Activation; Models, Molecular; Molecular Sequence Data; Phosphoprotein Phosphatases/chemistry; Phosphoprotein Phosphatases/metabolism; Phosphorylation; Protein Kinases/chemistry; Protein Kinases/genetics; Protein Kinases/metabolism; Protein Structure, Tertiary; Sequence Deletion; Signal Transduction
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
ARATH:SRK2E		GO:0046777: protein autophosphorylation	ECO:0000314:		P		MS analysis confirms that certain Ser/Thr residues were phosphorylated in recombinantly expressed SnRK2.6 (Supp. Fig. 1B). This analysis was performed after SnRK2.6 was purified after dephosphorylation by ABI1. The ratios of phosphorylated peptides to unmodified peptides (this data can elucidate the identity of potential phosphorylated residues of interest)were determined based on ion intensities of targeted peptides at different time points. One can see that S175 was the dominant phosphorylation site.	complete CACAO 5625
ARATH:SRK2E		GO:0004672: protein kinase activity	ECO:0000314:		F		Figure 1C shows the results of a kinetics experiment that shows that wild type SnRK2.6 phosphorylates ABF2, thus, kinase activity.	complete CACAO 5953
ARATH:SRK2E	involved_in	GO:0046777: protein autophosphorylation	ECO:0000314: direct assay evidence used in manual assertion		P		Seeded From UniProt	complete
ARATH:P2C56	enables	GO:0004721: phosphoprotein phosphatase activity	ECO:0000314: direct assay evidence used in manual assertion		F		Seeded From UniProt	complete
ARATH:P2C56	involved_in	GO:0006470: protein dephosphorylation	ECO:0000314: direct assay evidence used in manual assertion		P		Seeded From UniProt	complete
ARATH:P2C56		GO:0006470: protein dephosphorylation	ECO:0000314:		P		Figure 1D shows results of a kinetics experiment that show that ABI1 dephosphorylates phospho-SnRK2.6 in vitro.	complete CACAO 5951
ARATH:P2C56		GO:0004721: phosphoprotein phosphatase activity	ECO:0000314:		F		Figure 1D shows the results of a kinetics experiment that shows that ABI1 cleaves a phosphate off of the phosphoprotein pSnRK2.6	complete CACAO 5952

References

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