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Synapsin I: an actin-bundling protein under phosphorylation control

Synapsin I is a neuronal phosphoprotein comprised of two closely related polypeptides with apparent molecular weights of 78,000 and 76,000. It is found in association with the small vesicles clustered at the presynaptic junction. Its precise role is unknown, although it probably participates in vesi...

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Formato: Texto
Lenguaje:English
Publicado: The Rockefeller University Press 1987
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2114810/
https://www.ncbi.nlm.nih.gov/pubmed/3115996
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description Synapsin I is a neuronal phosphoprotein comprised of two closely related polypeptides with apparent molecular weights of 78,000 and 76,000. It is found in association with the small vesicles clustered at the presynaptic junction. Its precise role is unknown, although it probably participates in vesicle clustering and/or release. Synapsin I is known to associate with vesicle membranes, microtubules, and neurofilaments. We have examined the interaction of purified phosphorylated and unphosphorylated bovine and human synapsin I with tubulin and actin filaments, using cosedimentation, viscometric, electrophoretic, and morphologic assays. As purified from brain homogenates, synapsin I decreases the steady-state viscosity of solutions containing F-actin, enhances the sedimentation of actin, and bundles actin filaments. Phosphorylation by cAMP-dependent kinase has minimal effect on this interaction, while phosphorylation by brain extracts or by purified calcium- and calmodulin-dependent kinase II reduces its actin-bundling and -binding activity. Synapsin's microtubule-binding activity, conversely, is stimulated after phosphorylation by the brain extract. Two complementary peptide fragments of synapsin generated by 2-nitro-5-thiocyanobenzoic cleavage and which map to opposite ends of the molecule participate in the bundling process, either by binding directly to actin or by binding to other synapsin I molecules. 2-Nitro-5-thiocyanobenzoic peptides arising from the central portion of the molecule demonstrate neither activity. In vivo, synapsin I may link small synaptic vesicles to the actin-based cortical cytoskeleton, and coordinate their availability for release in a Ca++-dependent fashion.
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spelling pubmed-21148102008-05-01 Synapsin I: an actin-bundling protein under phosphorylation control J Cell Biol Articles Synapsin I is a neuronal phosphoprotein comprised of two closely related polypeptides with apparent molecular weights of 78,000 and 76,000. It is found in association with the small vesicles clustered at the presynaptic junction. Its precise role is unknown, although it probably participates in vesicle clustering and/or release. Synapsin I is known to associate with vesicle membranes, microtubules, and neurofilaments. We have examined the interaction of purified phosphorylated and unphosphorylated bovine and human synapsin I with tubulin and actin filaments, using cosedimentation, viscometric, electrophoretic, and morphologic assays. As purified from brain homogenates, synapsin I decreases the steady-state viscosity of solutions containing F-actin, enhances the sedimentation of actin, and bundles actin filaments. Phosphorylation by cAMP-dependent kinase has minimal effect on this interaction, while phosphorylation by brain extracts or by purified calcium- and calmodulin-dependent kinase II reduces its actin-bundling and -binding activity. Synapsin's microtubule-binding activity, conversely, is stimulated after phosphorylation by the brain extract. Two complementary peptide fragments of synapsin generated by 2-nitro-5-thiocyanobenzoic cleavage and which map to opposite ends of the molecule participate in the bundling process, either by binding directly to actin or by binding to other synapsin I molecules. 2-Nitro-5-thiocyanobenzoic peptides arising from the central portion of the molecule demonstrate neither activity. In vivo, synapsin I may link small synaptic vesicles to the actin-based cortical cytoskeleton, and coordinate their availability for release in a Ca++-dependent fashion. The Rockefeller University Press 1987-09-01 /pmc/articles/PMC2114810/ /pubmed/3115996 Text en This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 4.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/4.0/).
spellingShingle Articles
Synapsin I: an actin-bundling protein under phosphorylation control
title Synapsin I: an actin-bundling protein under phosphorylation control
title_full Synapsin I: an actin-bundling protein under phosphorylation control
title_fullStr Synapsin I: an actin-bundling protein under phosphorylation control
title_full_unstemmed Synapsin I: an actin-bundling protein under phosphorylation control
title_short Synapsin I: an actin-bundling protein under phosphorylation control
title_sort synapsin i: an actin-bundling protein under phosphorylation control
topic Articles
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2114810/
https://www.ncbi.nlm.nih.gov/pubmed/3115996