Colocalization on the same synaptic vesicles of syntaxin and SNAP-25 with synaptic vesicle proteins: a re-evaluation of functional models required?

Neurosci Res. 1996 Oct;26(2):141-8. doi: 10.1016/s0168-0102(96)01086-3.

Abstract

Synaptic vesicle docking and calcium dependent exocytosis are thought to require the specific interaction of proteins of the synaptic vesicle membrane (such as VAMP/synaptobrevin and synaptotagmin) and their plasma membrane-located counterparts (such as syntaxin and SNAP-25). When isolating synaptic vesicles by glycerol velocity gradient centrifugation we found cosedimentation of the presumptive presynaptic plasma membrane proteins syntaxin and SNAP-25 with synaptic vesicle membrane proteins. In order to further identify the antibody binding organelles we performed an immunoelectron microscopical analysis of synaptosomal profiles. Syntaxin and SNAP-25 were not only associated with the plasma membrane but to a large extent also with synaptic vesicle profiles. In order to answer the question whether the syntaxin and SNAP-25 containing vesicular compartment would also carry classical synaptic vesicle membrane markers we performed double labeling experiments using poly- and monoclonal antibodies. We found colocalization on the same vesicle not only of SNAP-25 and syntaxin but also of SNAP-25 with the synaptic vesicle membrane proteins SV2 and synaptotagmin and of syntaxin with the vesicular membrane protein synaptophysin. Our results demonstrate that syntaxin and SNAP-25 are colocalized with classical vesicle membrane proteins on the same vesicle and suggest that the functional models for the interaction of presynaptic proteins need to be re-evaluated.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Brain Chemistry*
  • Immunoblotting
  • Membrane Proteins / analysis*
  • Microscopy, Immunoelectron
  • Nerve Tissue Proteins / analysis*
  • Qa-SNARE Proteins
  • Rats
  • Synaptic Vesicles / chemistry*
  • Synaptophysin / analysis
  • Synaptosomal-Associated Protein 25

Substances

  • Membrane Proteins
  • Nerve Tissue Proteins
  • Qa-SNARE Proteins
  • Snap25 protein, rat
  • Synaptophysin
  • Synaptosomal-Associated Protein 25