The effect of synapsin I phosphorylation upon binding of synaptic vesicles to spectrin. |
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Authors: | A F Sikorski S R Goodman |
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Institution: | Department of Structural and Cellular Biology, University of South Alabama, College of Medicine, Mobile 36688. |
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Abstract: | We have previously demonstrated that brain spectrin is attached to small spherical synaptic vesicles via synapsin I. These studies utilized a novel microfiltration assay in which 125I-labelled synaptic vesicles were incubated with brain spectrin which was covalently attached to cellulosic membranes. In these studies purified dephosphosynapsin I was demonstrated to competitively inhibit the binding of the synaptic vesicles to the immobilized brain spectrin with a KI = 45 nM. In the current study we demonstrate that phosphorylation of synapsin I site 1 (0.74 mol Pi/mol synapsin I) with cAMP-dependent protein kinase and sites 2 and 3 (2.0 mol Pi/mol synapsin I) with Ca(2+)-calmodulin kinase II had little effect upon its interaction with brain spectrin. cAMP-dependent protein kinase phosphorylated synapsin I and Ca(2+)-calmodulin kinase II phosphorylated synapsin I both inhibited the binding of 125I-labelled synaptic vesicles to immobilized brain spectrin with a KI of 23 nM and 24 nM respectively. We conclude that phosphorylation of synapsin I does not down-regulate the interaction of synaptic vesicles with brain spectrin. |
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