title: Characterization of Arabidopsis calcium-dependent protein kinases: activated or not by calcium?
abstract: CDPKs (calcium-dependent protein kinases), which contain both calmodulin-like calcium binding and serine/threonine protein kinase domains, are only present in plants and some protozoans. Upon activation by a stimulus, they transduce the signal through phosphorylation cascades to induce downstream responses, including transcriptional regulation. To understand the functional specificities of CDPKs, 14 Arabidopsis CPKs (CDPKs in plants) representative of the three main subgroups were characterized at the biochemical level, using HA (haemagglutinin)-tagged CPKs expressed in planta. Most of them were partially or mainly associated with membranes, in agreement with acylation predictions. Importantly, CPKs displayed highly variable calcium-dependences for their kinase activities: seven CPKs from subgroups 1 and 2 were clearly sensitive to calcium with different intensities, whereas six CPKs from subgroup 3 exhibited low or no calcium sensitivity to two generic substrates. Interestingly, this apparent calcium-independence correlated with significant alterations in the predicted EF-hands of these kinases, although they all bound calcium. The noticeable exception, CPK25, was calcium-independent owing to the absence of functional EF-hands. Taken together, the results of the present study suggest that calcium binding differentially affects CDPK isoforms that may be activated by distinct molecular mechanisms.
authors: Institut des Sciences du Végétal, UPR 2355, CNRS, 1 av. de la terrasse, 91198 Gif s/Yvette cedex, France. boudsocq@evry.inra.fr
authors: Marie
authors: M
authors: Boudsocq
authors: Marie-Jo
authors: MJ
authors: Droillard
authors: Leslie
authors: L
authors: Regad
authors: Christiane
authors: C
authors: Laurière
mesh_terms: D017360:Arabidopsis / Q000201:enzymology*; D029681:Arabidopsis Proteins / Q000378:metabolism; D002118:Calcium / Q000502:physiology*; D002147:Calmodulin / Q000378:metabolism; D020832:EF Hand Motifs; D004789:Enzyme Activation; D007527:Isoenzymes / Q000378:metabolism; D030821:Plants, Genetically Modified; D011494:Protein Kinases / Q000378:metabolism*; D017871:Calcium-Calmodulin-Dependent Protein Kinases
chemical_list: D029681:Arabidopsis Proteins; D002118:Calcium; D002147:Calmodulin; D007527:Isoenzymes; D011494:Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases