Synaptotagmin is endogenously phosphorylated by Ca2+/calmodulin protein kinase II in synaptic vesicles.
The cytoplasmic domain of synaptotagmin (a synaptic vesicle-specific protein) has a high degree of homology with the Ca(2+)-phospholipid binding domain of protein kinase C. The Ca(2+)-phospholipid binding activity of synaptotagmin has been implicated in the docking and fusion of synaptic vesicles with the presynaptic membrane during Ca(2+)-induced exocytosis. The protein sequence contains potential phosphorylation sites for various protein kinases which could modulate its binding activity. At present there is no clear evidence that the protein is endogenously phosphorylated in intact vesicles. Here it is reported that phospho-synaptotagmin was immunoprecipitated from endogenously phosphorylated synaptic vesicles. The conditions used indicate that synaptotagmin, as synapsin I, is phosphorylated by Ca2+/calmodulin-dependent protein kinase II.
Laboratory of Neurochemistry, II School of Medicine, Naples, Italy.
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Popoli
D000818:Animals; D002135:Calcium-Binding Proteins; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D008562:Membrane Glycoproteins / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D010766:Phosphorylation; D011233:Precipitin Tests; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D013572:Synaptic Vesicles / Q000378:metabolism*; D050857:Synaptotagmins
D002135:Calcium-Binding Proteins; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D050857:Synaptotagmins; D011494:Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases