CALMODULIN DEPENDENT KINASE AND SYNAPTIC FUNCTION

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A Type II calcium/calmodulin-dependent protein kinase (CaM kinase II) that phosphorylates cytoskeletal proteins as major substrates in highly concentrated in neurons, including the postsynaptic density (PSD). The holoenzyme contains two autophosphorylating, calmodulin-binding subunits of 50 KDa and 60 KDa that are differentially expressed during development and exist in variable proportions in different brain regions. One goal of the proposed project is to determine if each subunit functions autonomously. The major 50 KDa subunit is the major postsynaptic density protein (mPSDp) that comprises 16-50% of the PSD. The amount of 50 KDa/mPSDp in the PSD is altered during post-natal development, sensory deprivation, and when animals are placed in enriched environments, suggesting that CaM kinase II plays an important role in synaptic function. Also present at the synapse are the microtubule-associated protein 2 (MAP 2) and neurofilament (NF) proteins, which are cytoskeletal protein substrates for the kinase. Both MAP 2 and NF are phosphorylated in vivo, but the site specificity, effect of phosphorylation, or physiologically relevant kinase involved are unknown. A second goal is to determine the effects of CaM kinase II on the function of these proteins. Also, i is not known whether changes in the phosphorylation state of the kinase and/or its substrate proteins affects synaptic function. The final goals of the project are to determine whether CaM kinase II in the PSD is altered compared to the cytosolic kinase, and to develop a model to elucidate the role of CaM kinase II in synaptic function. The working hypothesis in the present proposal is that CaM kinase II in the PSD is highly-phosphorylated, and that phosphorylation stabilizes the PSD as a structural component in neurons. Stabilization of the PSD may be important in the establishment and maintenance of synaptic contact between the pre- and postsynaptic neurons. Phosphorylation of endogenous MAP 2 is expected to reduce MAP 2/protein and MAP 2/membrane interactions which may be important for protein and membrane turnover. Phosphorylation of neurofilament proteins by CaM kinase II may stabilize neurofilaments. The proposed project will contribute to our understanding of several neurological disorders where alterations in the neuronal cytoskeleton and/or synaptic neurotransmission are observed, including Alzheimer's disease, epilepsy amyotrophic lateral sclerosis and the Guam form of Parkinsonism.