Effects of the neuronal phosphoprotein synapsin I on actin polymerization. I. Evidence for a phosphorylation-dependent nucleating effect

Synapsin I is a synaptic vesicle-specific phosphoprotein which is able to bind and bundle actin filaments in a phosphorylation-dependent fashion. In the present paper we have analyzed the effects of synapsin I on the kinetics of actin polymerization and their modulation by site-specific phosphorylat...

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Bibliographic Details
Published in:The Journal of biological chemistry 1992-06, Vol.267 (16), p.11281-11288
Main Authors: VALTORTA, F, GREENGARD, P, FESCE, R, CHIEREGATTI, E, BENFENATI, F
Format: Article
Language:English
Subjects:
Actins - metabolism
Actins - ultrastructure
Analytical, structural and metabolic biochemistry
Biological and medical sciences
Calcium-Calmodulin-Dependent Protein Kinases
Cations
Contractile proteins
Electrophoresis, Polyacrylamide Gel
Fundamental and applied biological sciences. Psychology
Holoproteins
Kinetics
Magnesium Chloride
Microscopy, Electron
Neurons - metabolism
Osmolar Concentration
Phosphorylation
Polymers
Potassium Chloride
Protein Kinases - metabolism
Proteins
Spectrometry, Fluorescence
Synapsins - metabolism
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Summary:Synapsin I is a synaptic vesicle-specific phosphoprotein which is able to bind and bundle actin filaments in a phosphorylation-dependent fashion. In the present paper we have analyzed the effects of synapsin I on the kinetics of actin polymerization and their modulation by site-specific phosphorylation of synapsin I. We found that dephosphorylated synapsin I accelerates the initial rate of actin polymerization and decreases the rate of filament elongation. The effect was observed at both low and high ionic strength, was specific for synapsin I, and was still present when polymerization was triggered by F-actin seeds. Dephosphorylated synapsin I was also able to induce actin polymerization and bundle formation in the absence of KCl and MgCl2. The effects of synapsin I were strongly decreased after its phosphorylation by Ca2+/calmodulin-dependent protein kinase II. These observations suggest that synapsin I has a phosphorylation-dependent nucleating effect on actin polymerization. The data are compatible with the view that changes in the phosphorylation state of synapsin I play a functional role in regulating the interactions between the nerve terminal cytoskeleton and synaptic vesicles in various stages of the exoendocytotic cycle.
ISSN:0021-9258
1083-351X
DOI:10.1016/s0021-9258(19)49908-0