Synaptic core complex of synaptobrevin, syntaxin, and SNAP25 forms high affinity alpha-SNAP binding site.
SNAPs (soluble NSF attachment proteins) are cytoplasmic proteins that bind to specific membrane receptors and mediate the membrane binding of NSF (N-ethylmaleimide-sensitive factor), a protein that is required for membrane fusion reactions. Three synaptic proteins in brain (SNAP25 (synaptosomal-associated protein of 25 kDa; no relation to the SNAPs for NSF), synaptobrevin/VAMP, and syntaxin) were identified as SNAP receptors by affinity chromatography on immobilized alpha-SNAP complexed to NSF (Söllner, T., Whiteheart, S. W., Brunner, M., Erdjument-Bromage, H., Geromanos, S., Tempst, P. and Rothman, J. E. (1993) Nature 362, 318-324). However, the nature of the alpha-SNAP binding site is unclear. We now show that alpha-SNAP binds tightly to the complex of syntaxin with synaptobrevin. SNAP25 is not required for tight binding of alpha-SNAP to this complex but stabilizes the syntaxin-synaptobrevin complex by forming a trimeric core complex with it. alpha-SNAP does not bind to synaptobrevin individually and binds only weakly to syntaxin and SNAP25 in the absence of synaptobrevin. These data suggest that the complex of the vesicular protein synaptobrevin with the plasma membrane protein syntaxin is required for physiological alpha-SNAP binding. Thus, alpha-SNAP probably functions in a late step of the membrane fusion reaction after the formation of the synaptobrevin-syntaxin-SNAP25 core complex.
McMahon
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HT
Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas 75235.
Südhof
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TC
D002352:Carrier Proteins / Q000378:metabolism; D005089:Exocytosis; D046911:Macromolecular Substances; D008565:Membrane Proteins / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D011485:Protein Binding; D050765:Qa-SNARE Proteins; D050683:R-SNARE Proteins; D011994:Recombinant Proteins; D052067:Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins; D013572:Synaptic Vesicles / Q000378:metabolism*; D050825:Synaptosomal-Associated Protein 25; D051040:Vesicle-Associated Membrane Protein 3; D033921:Vesicular Transport Proteins
D002352:Carrier Proteins; D046911:Macromolecular Substances; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D050765:Qa-SNARE Proteins; D050683:R-SNARE Proteins; D011994:Recombinant Proteins; D052067:Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins; D050825:Synaptosomal-Associated Protein 25; D051040:Vesicle-Associated Membrane Protein 3; D033921:Vesicular Transport Proteins