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Synapsin I is a microtubule-bundling protein

Nature volume 319, pages 145–147 (1986)Cite this article

Abstract

Synapsin I, a synaptic vesicle protein, is thought to be involved in the regulation of neurotransmission through its phosphorylation by the cyclic AMP-dependent and Ca2+/calmodulin-dependent protein kinases which become activated upon depolarization of nerve endings1–3. However, despite its recent characterization4 as a spectrin-binding protein immunologically related to erythrocyte protein 4.1, other interactions of synapsin I with structural proteins remain unknown. We report here that synapsin I can co-cycle with microtubules through three cycles of warm polymerization and cold depolymerization. Synapsin I binds saturably to microtubules stabilized by taxol, with an estimated dissociation constant (Kd) of 4.5µM and a stoichiometry of 1.2 mol of synapsin binding sites per mol tubulin dimer. Synapsin I also increases the turbidity of tubulin solutions at 37 °C, but without causing detectable alterations in the critical concentration required for polymerization. Mixtures of synapsin I and tubulin observed by negative stain electron microscopy contain bundles of microtubules, accounting for the effect of synapsin I on tubulin turbidity. Synapsin I is thus a candidate to mediate or regulate the interaction of synaptic vesicles with microtubules.

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  1. Anthony J. Baines

    Present address: University of Kent, Canterbury, UK

Authors and Affiliations

  1. Department of Cell Biology and Anatomy, Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, Maryland, 21205, USA

    Anthony J. Baines & Vann Bennett

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  1. Anthony J. Baines
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  2. Vann Bennett
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Baines, A., Bennett, V. Synapsin I is a microtubule-bundling protein. Nature 319, 145–147 (1986). https://doi.org/10.1038/319145a0

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