Munc13 binds and recruits SNAP25 to chaperone SNARE complex assembly

Kalayanasundaram, R. V.; Jin, H.; Li, F.; Shu, T.; Coleman, J.; Yang, J.; Pincet, F.; Zhang, Y.; Krishnakumar, S. S.; Rothman, J. E.

doi:10.1101/2020.08.19.257261

bioRxiv · 10.1101/2020.08.19.257261

Munc13 binds and recruits SNAP25 to chaperone SNARE complex assembly

Kalayanasundaram, R. V.·Jin, H.·Li, F.·Shu, T.·Coleman, J.·Yang, J.·Pincet, F.·Zhang, Y.·Krishnakumar, S. S.·Rothman, J. E.

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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 Munc13-1s capacity to bind all three synaptic SNARE proteins likely underlie its chaperone function.

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Kalayanasundaram, R. V., Jin, H., Li, F., Shu, T., Coleman, J., Yang, J., Pincet, F., Zhang, Y., Krishnakumar, S. S., Rothman, J. E.. 2020-08-19. Munc13 binds and recruits SNAP25 to chaperone SNARE complex assembly. https://doi.org/10.1101/2020.08.19.257261

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