Calcium Binds Dynamin I and Inhibits Its GTPase Activity |
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Authors: | Jun-Ping Liu,Qun-Xing Zhang,&dagger Graham Baldwin, Phillip J. Robinson |
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Affiliation: | Endocrine Unit, John Hunter Hospital, Newcastle, New South Wales;and; Ludwig Institute for Cancer Research, Royal Melbourne Hospital, Melbourne;and; Department of Surgery, Austin Hospital, Heidelberg, Victoria, Australia |
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Abstract: | Abstract: Synaptic vesicle recycling is a neuronal specialization of endocytosis that requires the GTPase activity of dynamin I and is triggered by membrane depolarization and Ca2+ entry. To establish the relationship between dynamin I GTPase activity and Ca2+, we used purified dynamin I and analyzed its interaction with Ca2+ in vitro. We report that Ca2+ bound to dynamin I and this was abolished by deletion of dynamin's C-terminal tail. Phosphorylation of dynamin I by protein kinase C promoted formation of a dynamin I tetramer and increased Ca2+ binding to the protein. Moreover, Ca2+ inhibited dynamin I GTPase activity after stimulation by phosphorylation or by phospholipids but not after stimulation with a GST-SH3 fusion protein containing the SH3 domain of phosphoinositide 3-kinase. These results suggest that in resting nerve terminals, phosphorylation of dynamin I by protein kinase C converts it to a tetramer that functions as a Ca2+-sensing protein. By binding to Ca2+, dynamin I GTPase activity is specifically decreased, possibly to regulate synaptic vesicle recycling. |
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Keywords: | Dynamin Calcium Protein kinase C Phosphorylation Synaptic vesicle recycling Neurotransmission |
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