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Regulation of Synaptotagmin I Phosphorylation by Multiple Protein Kinases
Author(s) -
Hilfiker Sabine,
Pieribone Vincent A.,
Nordstedt Christer,
Greengard Paul,
Czernik Andrew J.
Publication year - 1999
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1999.0730921.x
Subject(s) - synaptotagmin 1 , protein kinase c , phosphorylation , casein kinase 1 , microbiology and biotechnology , synaptic vesicle , protein phosphorylation , kinase , biology , biochemistry , protein kinase a , chemistry , vesicle , membrane
: Synaptotagmin I has been suggested to function as a low‐affinity calcium sensor for calcium‐triggered exocytosis from neurons and neuroendocrine cells. We have studied the phosphorylation of synaptotagmin I by a variety of protein kinases in vitro and in intact preparations. Syntagl, the purified, recombinant, cytoplasmic domain of rat synaptotagmin I, was an effective substrate in vitro for Ca 2+ /calmodulin‐dependent protein kinase II (CaMKII), protein kinase C (PKC), and casein kinase II (caskII). Sequencing of tryptic phosphopeptides from syntagl revealed that CaMKII and PKC phosphorylated the same residue, corresponding to Thr 112 , whereas CaskII phosphorylated two residues, corresponding to Thr 125 and Thr 128 . Endogenous synaptotagmin I was phosphorylated on purified synaptic vesicles by all three kinases. In contrast, no phosphorylation was observed on clathrin‐coated vesicles, suggesting that phosphorylation of synaptotagmin I in vivo occurs only at specific stage(s) of the synaptic vesicle life cycle. In rat brain synaptosomes and PC12 cells, K + ‐evoked depolarization or treatment with phorbol ester caused an increase in the phosphorylation state of synaptotagmin I at Thr 112 . The results suggest the possibility that the phosphorylation of synaptotagmin I by CaMKII and PKC contributes to the mechanism(s) by which these two kinases regulate neurotransmitter release.