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Homo- and heterooligomeric SNARE complexes studied by site-directed spin labeling.
Journal of Biological Chemistry
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SNARE (soluble NSF acceptor protein receptor) proteins are thought to mediate membrane fusion by assembling into heterooligomeric complexes that connect the fusing membranes and initiate the fusion reaction. Here we used site-directed spin labeling to map conformational changes that occur upon homo- and heterooligomeric complex formation of neuronal SNARE proteins. We found that the soluble domains of synaptobrevin, SNAP-25, and syntaxin 1 are unstructured. At higher concentrations, the SNARE motif of syntaxin 1 forms homooligomeric helical bundles with at least some of the alpha-helices aligned in parallel. In the assembled SNARE complex, mapping of thirty side chain positions yielded spectra which are in good agreement with the recently published crystal structure. The loop region of SNAP-25 that connects the two SNARE motifs is largely unstructured. C-terminal truncation of synaptobrevin resulted in complexes that are completely folded N-terminal of the truncation but become unstructured at the C-terminal end. The binary complex of syntaxin and SNAP-25 consists of a parallel four helix-bundle with properties resembling that of the ternary complex.
Amino Acid Substitution, Antigens, Surface/chemistry, Antigens, Surface/metabolism, Binding Sites, Cysteine, Electron Spin Resonance Spectroscopy, Macromolecular Substances, Membrane Fusion, Membrane Proteins/chemistry, Membrane Proteins/metabolism, Models, Molecular, Mutagenesis, Site-Directed, Nerve Tissue Proteins/chemistry, Nerve Tissue Proteins/metabolism, Peptide Fragments/chemistry, Protein Conformation, Protein Structure, Secondary, R-SNARE Proteins, SNARE Proteins, Sequence Deletion, Spin Labels, Synaptosomal-Associated Protein 25, Syntaxin 1, Vesicular Transport Proteins
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