This review discusses the properties and the role of Ca2+/calmodulin-regulated protein kinases, especially the Ca2+/calmodulin-dependent protein kinase II, the myosin light chain kinase and the myosin-associated giant protein kinase in insects. The general role of Ca2+/calmodulin-dependent protein kinases is to conduct and amplify signals within the cell, and to act as a potential switch in cross-talk regulation. Although being regulated by the same second messenger complex the Ca2+/calmodulin-regulated protein kinases differ remarkably in subsequent regulation, kinetics, substrate specificity, size, localization, and expression. Ca2+/cal- modulin-dependent protein kinase II belongs to one of the major classes of protein kinases in cellular signal transduction. It is predominantly found in the head region of Drosophila and considered as an important part in neural development, and synaptic transmission with consequences in learning and behavior. In muscle cells different Ca2+/calmodulin-regulated protein kinases are involved in muscle contraction. The myosin light chain kinase phosphorylates in a Ca2+/calmodulin-dependent manner the regulatory light chain of myosin to facilitate the flight function of insects. An enigmatic protein kinase remains the 900 kDa myosin-associated protein kinase projectin which belongs to the subfamily of myosin light chain kinases. The regulation and function of projectin remains unclear.
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