Synapsin I is a microtubule-bundling protein

Nature. 1986 Jan 9-15;319(6049):145-7. doi: 10.1038/319145a0.


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 endings. However, despite its recent characterization 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 4.5 microM 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 degrees 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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Alkaloids / pharmacology
  • Animals
  • Axonal Transport
  • Brain Chemistry
  • Cattle
  • Microscopy, Electron
  • Microtubule-Associated Proteins / metabolism*
  • Nerve Tissue Proteins / metabolism*
  • Paclitaxel
  • Protein Binding
  • Synapsins
  • Synaptic Vesicles*
  • Tubulin / metabolism


  • Alkaloids
  • Microtubule-Associated Proteins
  • Nerve Tissue Proteins
  • Synapsins
  • Tubulin
  • Paclitaxel