title: Calcium-stimulated autophosphorylation site of plant chimeric calcium/calmodulin-dependent protein kinase.
abstract: The existence of two molecular switches regulating plant chimeric Ca(2+)/calmodulin-dependent protein kinase (CCaMK), namely the C-terminal visinin-like domain acting as Ca(2+)-sensitive molecular switch and calmodulin binding domain acting as Ca(2+)-stimulated autophosphorylation-sensitive molecular switch, has been described (Sathyanarayanan, P. V., Cremo, C. R., and Poovaiah, B. W. (2000) J. Biol. Chem. 275, 30417-30422). Here we report the identification of Ca(2+)-stimulated autophosphorylation site of CCaMK by matrix-assisted laser desorption ionization time of flight-mass spectrometry. Thr(267) was confirmed as the Ca(2+)-stimulated autophosphorylation site by post-source decay experiments and by site-directed mutagenesis. The purified T267A mutant form of CCaMK did not show Ca(2+)-stimulated autophosphorylation, autophosphorylation-dependent variable calmodulin affinity, or Ca(2+)/calmodulin stimulation of kinase activity. Sequence comparison of CCaMK from monocotyledonous plant (lily) and dicotyledonous plant (tobacco) suggests that the autophosphorylation site is conserved. This is the first identification of a phosphorylation site specifically responding to activation by second messenger system (Ca(2+) messenger system) in plants. Homology modeling of the kinase and calmodulin binding domain of CCaMK with the crystal structure of calcium/calmodulin-dependent protein kinase 1 suggests that the Ca(2+)-stimulated autophosphorylation site is located on the surface of the kinase and far from the catalytic site. Analysis of Ca(2+)-stimulated autophosphorylation with increasing concentration of CCaMK indicates the possibility that the Ca(2+)-stimulated phosphorylation occurs by an intermolecular mechanism.
authors.affiliation: Laboratory of Plant Molecular Biology and Physiology, Department of Horticulture,Washington State University, Pullman, Washington 99164, USA.
authors.forename: P V
authors.initials: PV
authors.lastname: Sathyanarayanan
authors.forename: W F
authors.initials: WF
authors.lastname: Siems
authors.forename: J P
authors.initials: JP
authors.lastname: Jones
authors.forename: B W
authors.initials: BW
authors.lastname: Poovaiah
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000737:chemistry* / Q000378:metabolism*; D002846:Chromatography, Affinity; D007700:Kinetics; D019668:Liliaceae / Q000201:enzymology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010446:Peptide Fragments / Q000737:chemistry* / Q000302:isolation & purification; D010748:Phosphopeptides / Q000737:chemistry* / Q000302:isolation & purification; D010766:Phosphorylation; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D010446:Peptide Fragments; D010748:Phosphopeptides; D011993:Recombinant Fusion Proteins; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002118:Calcium