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A conformational switch in syntaxin during exocytosis: role of munc18
Author(s) -
Dulubova Irina,
Sugita Shuzo,
Hill Sandra,
Hosaka Masahiro,
Fernandez Imma,
Südhof Thomas C.,
Rizo Josep
Publication year - 1999
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1093/emboj/18.16.4372
Subject(s) - synaptobrevin , syntaxin , exocytosis , munc 18 , syntaxin 3 , snare complex , stx1a , biology , microbiology and biotechnology , transmembrane domain , transmembrane protein , secretion , biochemistry , synaptic vesicle , membrane , vesicle , receptor
Syntaxin 1, an essential protein in synaptic membrane fusion, contains a helical autonomously folded N‐terminal domain, a C‐terminal SNARE motif and a transmembrane region. The SNARE motif binds to synaptobrevin and SNAP‐25 to assemble the core complex, whereas almost the entire cytoplasmic sequence participates in a complex with munc18‐1, a neuronal Sec1 homolog. We now demonstrate by NMR spectroscopy that, in isolation, syntaxin adopts a ‘closed’ conformation. This default conformation of syntaxin is incompatible with core complex assembly which requires an ‘open’ syntaxin conformation. Using site‐directed mutagenesis, we find that disruption of the closed conformation abolishes the ability of syntaxin to bind to munc18‐1 and to inhibit secretion in PC12 cells. These results indicate that syntaxin binds to munc18‐1 in a closed conformation and suggest that this conformation represents an essential intermediate in exocytosis. Our data suggest a model whereby, during exocytosis, syntaxin undergoes a large conformational switch that mediates the transition between the syntaxin–munc18‐1 complex and the core complex.