| Structural highlights
Function
[CIPKO_ARATH] Involved in the regulatory pathway for the control of intracellular Na(+) and K(+) homeostasis and salt tolerance. Activates the vacuolar H(+)/Ca(2+) antiporter CAX1 and operates in synergy with CBL4/SOS3 to activate the plasma membrane Na(+)/H(+) antiporter SOS1. CIPK serine-threonine protein kinases interact with CBL proteins. Binding of a CBL protein to the regulatory NAF domain of CIPK protein lead to the activation of the kinase in a calcium-dependent manner. Phosphorylates CBL1, CBL4 and CBL10.[1] [2] [3] [4]
Publication Abstract from PubMed
Plant cells have developed specific protective molecular machinery against environmental stresses. The family of CBL-interacting protein kinases (CIPK) and their interacting activators, the calcium sensors calcineurin B-like (CBLs), work together to decode calcium signals elicited by stress situations. The molecular basis of biological activation of CIPKs relies on the calcium-dependent interaction of a self-inhibitory NAF motif with a particular CBL, the phosphorylation of the activation loop by upstream kinases, and the subsequent phosphorylation of the CBL by the CIPK. We present the crystal structures of the NAF-truncated and pseudophosphorylated kinase domains of CIPK23 and CIPK24/SOS2. In addition, we provide biochemical data showing that although CIPK23 is intrinsically inactive and requires an external stimulation, CIPK24/SOS2 displays basal activity. This data correlates well with the observed conformation of the respective activation loops: Although the loop of CIPK23 is folded into a well-ordered structure that blocks the active site access to substrates, the loop of CIPK24/SOS2 protrudes out of the active site and allows catalysis. These structures together with biochemical and biophysical data show that CIPK kinase activity necessarily requires the coordinated releases of the activation loop from the active site and of the NAF motif from the nucleotide-binding site. Taken all together, we postulate the basis for a conserved calcium-dependent NAF-mediated regulation of CIPKs and a variable regulation by upstream kinases.
Structural basis of the regulatory mechanism of the plant CIPK family of protein kinases controlling ion homeostasis and abiotic stress.,Chaves-Sanjuan A, Sanchez-Barrena MJ, Gonzalez-Rubio JM, Moreno M, Ragel P, Jimenez M, Pardo JM, Martinez-Ripoll M, Quintero FJ, Albert A Proc Natl Acad Sci U S A. 2014 Oct 6. pii: 201407610. PMID:25288725[5]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Halfter U, Ishitani M, Zhu JK. The Arabidopsis SOS2 protein kinase physically interacts with and is activated by the calcium-binding protein SOS3. Proc Natl Acad Sci U S A. 2000 Mar 28;97(7):3735-40. PMID:10725350 doi:http://dx.doi.org/10.1073/pnas.040577697
- ↑ Qiu QS, Guo Y, Dietrich MA, Schumaker KS, Zhu JK. Regulation of SOS1, a plasma membrane Na+/H+ exchanger in Arabidopsis thaliana, by SOS2 and SOS3. Proc Natl Acad Sci U S A. 2002 Jun 11;99(12):8436-41. Epub 2002 May 28. PMID:12034882 doi:http://dx.doi.org/10.1073/pnas.122224699
- ↑ Cheng NH, Pittman JK, Zhu JK, Hirschi KD. The protein kinase SOS2 activates the Arabidopsis H(+)/Ca(2+) antiporter CAX1 to integrate calcium transport and salt tolerance. J Biol Chem. 2004 Jan 23;279(4):2922-6. Epub 2003 Oct 28. PMID:14583601 doi:http://dx.doi.org/10.1074/jbc.M309084200
- ↑ Hashimoto K, Eckert C, Anschutz U, Scholz M, Held K, Waadt R, Reyer A, Hippler M, Becker D, Kudla J. Phosphorylation of calcineurin B-like (CBL) calcium sensor proteins by their CBL-interacting protein kinases (CIPKs) is required for full activity of CBL-CIPK complexes toward their target proteins. J Biol Chem. 2012 Mar 9;287(11):7956-68. doi: 10.1074/jbc.M111.279331. Epub 2012 , Jan 17. PMID:22253446 doi:http://dx.doi.org/10.1074/jbc.M111.279331
- ↑ Chaves-Sanjuan A, Sanchez-Barrena MJ, Gonzalez-Rubio JM, Moreno M, Ragel P, Jimenez M, Pardo JM, Martinez-Ripoll M, Quintero FJ, Albert A. Structural basis of the regulatory mechanism of the plant CIPK family of protein kinases controlling ion homeostasis and abiotic stress. Proc Natl Acad Sci U S A. 2014 Oct 6. pii: 201407610. PMID:25288725 doi:http://dx.doi.org/10.1073/pnas.1407610111
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