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  • Title: Munc18-bound syntaxin readily forms SNARE complexes with synaptobrevin in native plasma membranes.
    Author: Zilly FE, Sørensen JB, Jahn R, Lang T.
    Journal: PLoS Biol; 2006 Oct; 4(10):e330. PubMed ID: 17002520.
    Abstract:
    Munc18-1, a protein essential for regulated exocytosis in neurons and neuroendocrine cells, belongs to the family of Sec1/Munc18-like (SM) proteins. In vitro, Munc18-1 forms a tight complex with the SNARE syntaxin 1, in which syntaxin is stabilized in a closed conformation. Since closed syntaxin is unable to interact with its partner SNAREs SNAP-25 and synaptobrevin as required for membrane fusion, it has hitherto not been possible to reconcile binding of Munc18-1 to syntaxin 1 with its biological function. We now show that in intact and exocytosis-competent lawns of plasma membrane, Munc18-1 forms a complex with syntaxin that allows formation of SNARE complexes. Munc18-1 associated with membrane-bound syntaxin 1 can be effectively displaced by adding recombinant synaptobrevin but not syntaxin 1 or SNAP-25. Displacement requires the presence of endogenous SNAP-25 since no displacement is observed when chromaffin cell membranes from SNAP-25-deficient mice are used. We conclude that Munc18-1 allows for the formation of a complex between syntaxin and SNAP-25 that serves as an acceptor for vesicle-bound synaptobrevin and that thus represents an intermediate in the pathway towards exocytosis.
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