Disease relevance of CPK1

• To verify the kinase activity of the enzyme encoded by AK1, a fusion of an amino-terminally truncated AK1 to the C-terminus of glutathione S-transferase was expressed in Escherichia coli [1].

High impact information on CPK1

• In Arabidopsis thaliana, the analysis of 42 isoforms of CDPK and related kinases is expected to delineate Ca(2+) signalling pathways in all aspects of plant biology [2].
• Recent genetic evidence has revealed isoform-specific functions for a CDPK that is essential for Plasmodium berghei gametogenesis, and for a related chimeric Ca(2+) and calmodulin-dependent protein kinase (CCaMK) that is essential to the formation of symbiotic nitrogen-fixing nodules in plants [2].
• Here, we show that phosphorylation of its N-terminal regulatory domain by a Ca(2+)-dependent protein kinase (CDPK isoform CPK1), inhibits both basal activity ( approximately 10%) and calmodulin stimulation ( approximately 75%), as shown by Ca(2+)-transport assays with recombinant enzyme expressed in yeast [3].
• These results support the hypothesis that ACA2 activity is regulated as the balance between the initial kinetics of calmodulin stimulation and CDPK inhibition, providing an example in plants for a potential point of crosstalk between two different Ca(2+)-signaling pathways [3].
• A CDPK phosphorylation site was mapped to Ser(45) near a calmodulin binding site, using a fusion protein containing the N-terminal domain as an in vitro substrate for a recombinant CPK1 [3].

Biological context of CPK1

• The observation of a peroxisome-located CDPK suggests a mechanism for calcium regulation of peroxisomal functions involved in oxidative stress and lipid metabolism [4].
• The activity of calmodulin-like domain protein kinase (CDPK) is regulated by the direct binding of Ca2+ [5].
• Homologous genomic DNA sequences that hybridize with CRK cDNA but not with a carrot CDPK probe have been detected in a variety of higher plant taxa, including monocotyledonous species, suggesting that this CDPK-related kinase is widely conserved among angiosperms [6].
• Both the 14-3-3 binding and activation of CPK-1 were specifically disrupted by a known 14-3-3 binding peptide LSQRQRSTpSTPNVHMV (IC50 = 30 microM) [7].
• Our results show that ectopic expression of a heterologous CDPK can enhance NADPH oxidase activity and stimulate an oxidative burst in tomato protoplasts [8].

Anatomical context of CPK1

• Molecular identification of phenylalanine ammonia-lyase as a substrate of a specific constitutively active Arabidopsis CDPK expressed in maize protoplasts [9].
• This is the first demonstration of myristoylation of a CDPK protein which may contribute to the mechanism by which this protein is localized to the plasma membrane [10].
• CDPK enzymatic activity previously has been detected in many locations in plant cells, including the cytosol, the cytoskeleton, and the membrane fraction [11].
• This protein was confirmed to be a CDPK by mass spectrometry, possibly the red beet ortholog of rice CDPK2 and Arabidopsis thaliana CPK9, both found associated with membranes [12].

Associations of CPK1 with chemical compounds

• Identification of the specific CDPK as a PAL kinase now opens up the possibility of exploring the calcium link in biotic stress signalling, salicylate and phytoalexin production as well as the significance of PAL phosphorylation [9].
• We earlier reported that, of a wide array of lipids tested, only phosphatidylinositol and lysophosphatidylcholine stimulated histone phosphorylation by AK-1 [Harper, J. F., Binder, B. M., & Sussman M. R. (1993) Biochemistry 32, 3282-3290] [13].
• CDPK32 was shown to be induced by touch, wounding, NaCl and darkness while ethylene and MeJA had little or no effect [14].

Other interactions of CPK1

• We report here the X-ray crystal structure of the J-CaM-LD region of CDPK from Arabidopsis thaliana (AtCPK1), determined to 2.0 A resolution using multiple-wavelength anomalous dispersion (MAD) [15].

Analytical, diagnostic and therapeutic context of CPK1

• DNA cloning and Western blot analysis indicate that multiple CDPK isoforms are present in the model plant system Arabidopsis thaliana [1].

References