The effect of synapsin I phosphorylation upon binding of synaptic vesicles to spectrin.
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.
Sikorski
A F
AF
Department of Structural and Cellular Biology, University of South Alabama, College of Medicine, Mobile 36688.
Goodman
S R
SR
D000818:Animals; D001667:Binding, Competitive; D002417:Cattle; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D013049:Spectrin / Q000378:metabolism*; D016704:Synapsins / Q000378:metabolism*; D013572:Synaptic Vesicles / Q000378:metabolism*
D016704:Synapsins; D013049:Spectrin; D011494:Protein Kinases; D011493:Protein Kinase C