Autoinhibition of Munc18-1 modulates synaptobrevin binding and helps to enable Munc13-dependent regulation of membrane fusion

• Main Authors: Ewa Sitarska, Junjie Xu, Seungmee Park, Xiaoxia Liu, Bradley Quade, Karolina Stepien, Kyoko Sugita, Chad A Brautigam, Shuzo Sugita, Josep Rizo
• Format: Article
• Language: English
• Published: eLife Sciences Publications Ltd 2017-05-01
• Series: eLife
• Subjects: Munc18-1; Munc13; neurotransmitter release; autoinhibition; protein NMR
• Online Access: https://elifesciences.org/articles/24278

Munc18-1 orchestrates SNARE complex assembly together with Munc13-1 to mediate neurotransmitter release. Munc18-1 binds to synaptobrevin, but the relevance of this interaction and its relation to Munc13 function are unclear. NMR experiments now show that Munc18-1 binds specifically and non-specifically to synaptobrevin. Specific binding is inhibited by a L348R mutation in Munc18-1 and enhanced by a D326K mutation designed to disrupt the ‘furled conformation’ of a Munc18-1 loop. Correspondingly, the activity of Munc18-1 in reconstitution assays that require Munc18-1 and Munc13-1 for membrane fusion is stimulated by the D326K mutation and inhibited by the L348R mutation. Moreover, the D326K mutation allows Munc13-1-independent fusion and leads to a gain-of-function in rescue experiments in Caenorhabditis elegans unc-18 nulls. Together with previous studies, our data support a model whereby Munc18-1 acts as a template for SNARE complex assembly, and autoinhibition of synaptobrevin binding contributes to enabling regulation of neurotransmitter release by Munc13-1.