Structural basis for the inhibitory role of tomosyn in exocytosis

J Biol Chem. 2004 Nov 5;279(45):47192-200. doi: 10.1074/jbc.M408767200. Epub 2004 Aug 16.


Upon Ca2+ influx synaptic vesicles fuse with the plasma membrane and release their neurotransmitter cargo into the synaptic cleft. Key players during this process are the Q-SNAREs syntaxin 1a and SNAP-25 and the R-SNARE synaptobrevin 2. It is thought that these membrane proteins gradually assemble into a tight trans-SNARE complex between vesicular and plasma membrane, ultimately leading to membrane fusion. Tomosyn is a soluble protein of 130 kDa that contains a COOH-terminal R-SNARE motif but lacks a transmembrane anchor. Its R-SNARE motif forms a stable core SNARE complex with syntaxin 1a and SNAP-25. Here we present the crystal structure of this core tomosyn SNARE complex at 2.0-A resolution. It consists of a four-helical bundle very similar to that of the SNARE complex containing synaptobrevin. Most differences are found on the surface, where they prevented tight binding of complexin. Both complexes form with similar rates as assessed by CD spectroscopy. In addition, synaptobrevin cannot displace the tomosyn helix from the tight complex and vice versa, indicating that both SNARE complexes represent end products. Moreover, data bank searches revealed that the R-SNARE motif of tomosyn is highly conserved throughout all eukaryotic kingdoms. This suggests that the formation of a tight SNARE complex is important for the function of tomosyn.

MeSH terms

  • Adaptor Proteins, Vesicular Transport
  • Amino Acid Motifs
  • Amino Acid Sequence
  • Animals
  • Anisotropy
  • Antigens, Surface / chemistry
  • Binding Sites
  • Calcium / metabolism
  • Cell Membrane / metabolism
  • Circular Dichroism
  • Crystallography, X-Ray
  • Electrophoresis, Polyacrylamide Gel
  • Escherichia coli / metabolism
  • Exocytosis*
  • Membrane Fusion
  • Membrane Proteins / metabolism
  • Membrane Proteins / physiology*
  • Microscopy, Fluorescence
  • Models, Molecular
  • Molecular Sequence Data
  • Nerve Tissue Proteins / chemistry
  • Nerve Tissue Proteins / metabolism
  • Nerve Tissue Proteins / physiology*
  • Protein Conformation
  • Protein Structure, Tertiary
  • R-SNARE Proteins
  • Rats
  • Recombinant Proteins / chemistry
  • Sequence Homology, Amino Acid
  • Signal Transduction
  • Synaptosomal-Associated Protein 25
  • Syntaxin 1
  • Time Factors
  • Vesicular Transport Proteins / chemistry
  • Vesicular Transport Proteins / physiology*


  • Adaptor Proteins, Vesicular Transport
  • Antigens, Surface
  • Membrane Proteins
  • Nerve Tissue Proteins
  • R-SNARE Proteins
  • Recombinant Proteins
  • Snap25 protein, rat
  • Stx1a protein, mouse
  • Stx1a protein, rat
  • Synaptosomal-Associated Protein 25
  • Syntaxin 1
  • Vesicular Transport Proteins
  • complexin I
  • tomosyn protein, mouse
  • Calcium

Associated data

  • PDB/1URQ