1. Munc13 binds and recruits SNAP25 to chaperone SNARE complex assembly
- Author
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Jie Yang, Yongli Zhang, Jeff Coleman, Tong Shu, Fang Li, Huaizhou Jin, James E. Rothman, Shyam S. Krishnakumar, R. V. Kalayanasundaram, and Frederic Pincet
- Subjects
chemistry.chemical_compound ,Förster resonance energy transfer ,biology ,VAMP2 ,Chemistry ,Chaperone (protein) ,Vesicle ,biology.protein ,Phospholipid ,Biophysics ,SNAP25 ,Linker ,SNARE complex assembly - Abstract
Synaptic vesicle fusion is mediated by membrane-bridging complexes formed by SNARE proteins - VAMP2 on the vesicle and Syntaxin-1/SNAP25 on the pre-synaptic membrane. Accumulating evidence suggest that chaperones Munc18-1 and Munc13-1 co-operatively catalyze SNARE assembly via an intermediate ‘template’ complex containing Syntaxin-1 and VAMP2. How SNAP25 is chaperoned into this nascent complex remains a mystery. Here we report that Munc13-1 recruits SNAP25 to initiate the ternary SNARE complex assembly by direct binding, as judged by bulk FRET spectroscopy and single-molecule optical tweezer studies. Detailed structure-function analyses show that the binding is mediated by the Munc13-1 MUN domain and is specific for the SNAP25 ‘linker’ region that connects the two SNARE motifs. Consequently, freely diffusing SNAP25 molecules on phospholipid bilayers are concentrated and presumably bound in ~1:1 stoichiometry by the self-assembled Munc13-1 nanoclusters. Our data suggests that Munc13-1’s capacity to bind all three synaptic SNARE proteins likely underlie its chaperone function.
- Published
- 2020