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DECODING Ca²⁺ SIGNALS BY CHIMERIC Ca²⁺/CALMODULIN DEPENDENT PROTEIN KINASE. P.V. Sathyanarayanan and B.W. Poovaiah, Department of Horticulture, Washington State University, Pullman, WA.

     Chimeric Ca²⁺/dependent protein kinase (CCaMK) is characterized by a serine-threonine kinase domain, an autoinhibitory domain overlapping with the calmodulin (CaM) binding domain and a C-terminal visinin-like domain. Visinin-like proteins are high affinity Ca²⁺ binding proteins and function as Ca²⁺ sensors in neurons. We have shown that the visinin-like domain of CCaMK functions as Ca²⁺ sensitive switch regulating autophosphorylation  (J. Biol. Chem. 275:30417-30422, 2000). The Ca²⁺ stimulated autophosphorylation of Thr²⁶⁷ occurs by an intermolecular mechanism in the oligomeric complex (J. Biol. Chem. 2001, in press). The autophosphorylation leads to activation of kinase by significantly increasing the affinity for CaM. CaM itself acts as receptor for intracellular Ca²⁺ signals.  The CaM-binding leads to removal of autoinhibition making the kinase maximally active. CCaMK is able to decode Ca²⁺ signals in a two step process. In the first step mediated by the visinin-like domain, the Ca²⁺ signals are decoded in to autophosphorylation of the oligomeric kinase. This activation enables the kinase to further decode the signals into substrate phosphorylation. CCaMK is expressed in the root tips and pollen mother cells. These results suggest that CCaMK is involved in decoding tissue and development specific Ca²⁺ signals.

     (Supported by NASA grant NAG5-4841 and NSF grant MCB 0082256)