Calcium/calmodulin up-regulates a cytoplasmic receptor-like kinase in plants.
Calcium/calmodulin-dependent kinases play an important role in protein phosphorylation in eukaryotes. However, not much is known about calcium/calmodulin-dependent protein phosphorylation and its role in signal transduction in plants. By using a protein-protein interaction-based approach, we have isolated a novel plant-specific calmodulin-binding receptor-like cytoplasmic kinase (CRCK1) from Arabidopsis thaliana, as well as its ortholog from Medicago sativa (alfalfa). CRCK1 does not show high homology to calcium/calmodulin-dependent protein kinases in animals. In contrast, it shows high homology in the kinase domain to serine/threonine receptor-like kinases in plants. However, it contains neither a transmembrane domain nor an extracellular domain. Calmodulin binds to CRCK1 in a calcium-dependent manner with an affinity of approximately 20.5 nm. The calmodulin-binding site in CRCK1 is located in amino acids 160-183, which overlap subdomain II of the kinase domain. CRCK1 undergoes autophosphorylation in the presence of Mg2+ at the threonine residue(s). The Km and Vmax values of CRCK1 for ATP are 1 microm and 33.6 pmol/mg/min, respectively. Calcium/calmodulin stimulates the kinase activity of CRCK1, which increases the Vmax of CRCK1 approximately 9-fold. The expression of CRCK1 is increased in response to stresses such as cold and salt and stress molecules such as abscisic acid and hydrogen peroxide. These results indicate the presence of a calcium/calmodulin-regulated receptor-like cytoplasmic kinase in plants. Furthermore, these results also suggest that calcium/calmodulin-regulated protein phosphorylation involving CRCK1 plays a role in stress signal transduction in plants.
Center for Integrated Biotechnology and Department of Horticulture, Washington State University, Pullman, Washington 99164-6414, USA.
Tianbao
T
Yang
Shubho
S
Chaudhuri
Lihua
L
Yang
Yanping
Y
Chen
B W
BW
Poovaiah
D000040:Abscisic Acid / Q000737:chemistry; D000255:Adenosine Triphosphate / Q000737:chemistry; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology*; D029681:Arabidopsis Proteins / Q000096:biosynthesis* / Q000737:chemistry; D001665:Binding Sites; D015152:Blotting, Northern; D015153:Blotting, Western; D002118:Calcium / Q000737:chemistry / Q000378:metabolism*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000096:biosynthesis* / Q000737:chemistry; D002147:Calmodulin / Q000737:chemistry / Q000378:metabolism*; D020134:Catalytic Domain; D003001:Cloning, Molecular; D003593:Cytoplasm / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004247:DNA / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D005091:Exons; D006861:Hydrogen Peroxide / Q000737:chemistry / Q000494:pharmacology; D047468:Immunoprecipitation; D007700:Kinetics; D008274:Magnesium / Q000737:chemistry; D000455:Medicago sativa / Q000235:genetics; D008861:Microsomes / Q000378:metabolism; D008969:Molecular Sequence Data; D010766:Phosphorylation; D010770:Phosphotransferases / Q000378:metabolism*; D030821:Plants, Genetically Modified; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012313:RNA / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D013912:Threonine / Q000737:chemistry; D013997:Time Factors; D015854:Up-Regulation
D029681:Arabidopsis Proteins; D002147:Calmodulin; D011994:Recombinant Proteins; D013912:Threonine; D012313:RNA; D000040:Abscisic Acid; D000255:Adenosine Triphosphate; D004247:DNA; D006861:Hydrogen Peroxide; D010770:Phosphotransferases; C493166:CRCK1 protein, Arabidopsis; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D008274:Magnesium; D002118:Calcium