Ca2+/calmodulin-dependent protein kinase type-II (CaMK-II) is a Ser/Thr protein kinase regulated by Ca2+ and Calmodulin. It is a highly conserved and broadly expressed enzyme and has a unique structure and dynamic regulation. It has the ability to remain active in the absence of Ca 2+ as a result of Ca2+ dependent autophosphorylation. CaMK-II phospliorylates proteins involved in neurotransmitter secretion, long term potentiation, cytoskeletal dynamics, gene transcription, and cell motility. To support existing and identify new intracellular roles of CaMK-II, potential binding partners were identified. This was accomplished by transfecting and purifying FLAG-tagged CaMK-II\u27s (α, βE, δC, and δE). CaMK-II associated proteins were then identified using tandem mass spectrometry. Known binding partners were identified using this approach, including CaMK-II and calmodulin, verifying the approach\u27s validity. Additionally several unexpected but interesting proteins were identified, including the gelsolin related actin binding protein, Flightless-I. Fli-I is an actin binding and capping protein that also functions as a transcriptional coactivator. The CaMK-II-Fli-I interaction was confirmed with endogenous (un-tagged) proteins. The association and localization of Fli-I are dependent on CaMK-II\u27s activity state, although Fli-I is not a substrate of CaMK-II. When CaMK-II is inhibited, Fli-I translocates to the nucleus. Conversely when CaMK-II is artificially activated using a Ca2+ ionophore, Fli-I returns to the cytosol. The discovery of this reversible interaction epresents a potentially new CaMK-II regulated pathway and likely serves as a link between Ca2+ based signal transduction pathways and regulation of the actin component of the cytoskeleton and transcription
