title: Heterologous expression and biochemical characterization of two calcium-dependent protein kinase isoforms CaCPK1 and CaCPK2 from chickpea.
abstract: In plants, calcium-dependent protein kinases (CPKs) constitute a unique family of enzymes consisting of a protein kinase catalytic domain fused to carboxy-terminal autoregulatory and calmodulin-like domains. We isolated two cDNAs encoding calcium-dependent protein kinase isoforms (CaCPK1 and CaCPK2) from chickpea. Both isoforms were expressed as fusion proteins in Escherichia coli. Biochemical analyses have identified CaCPK1 and CaCPK2 as Ca(2+)-dependent protein kinases since both enzymes phosphorylated themselves and histone III-S as substrate only in the presence of Ca(2+). The kinase activity of the recombinant enzymes was calmodulin independent and sensitive to CaM antagonists W7 [N-(6-aminohexyl)-5-chloro-1-naphthalene sulphonamide] and calmidazoilum. Phosphoamino acid analysis revealed that the isoforms transferred the gamma-phosphate of ATP only to serine residues of histone III-S and their autophosphorylation occurred on serine and threonine residues. These two isoforms showed considerable variations with respect to their biochemical and kinetic properties including Ca(2+) sensitivities. The recombinant CaCPK1 has a pH and temperature optimum of pH 6.8-8.6 and 35-42 degrees C, respectively, whereas CaCPK2 has a pH and temperature optimum of pH 7.2-9 and 35-42 degrees C, respectively. Taken together, our results suggest that CaCPK1 and CaCPK2 are functional serine/threonine kinases and may play different roles in Ca(2+)-mediated signaling in chickpea plants.
authors.affiliation: Department of Biochemistry, Indian Institute of Science, Bangalore-560 012, India.
authors.forename: S R
authors.initials: SR
authors.lastname: Syam Prakash
authors.forename: Chelliah
authors.initials: C
authors.lastname: Jayabaskaran
mesh_terms: D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000494:pharmacology; D029863:Cicer / Q000201:enzymology / Q000235:genetics*; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008969:Molecular Sequence Data; D010766:Phosphorylation; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D011494:Protein Kinases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013696:Temperature
chemical_list: D002147:Calmodulin; D007527:Isoenzymes; D010940:Plant Proteins; D011994:Recombinant Proteins; D011494:Protein Kinases