Autoinhibition of Munc18-1 modulates synaptobrevin binding and helps to enable Munc13-dependent regulation of membrane fusion
The diagram fusion assays between proteoliposomes containing synaptobrevin and proteoliposomes containing syntaxin-1-SNAP-25 complex in the presence of NSF, αSNAP, a Munc13-1 fragment and WT or mutant Munc18-1. The D326K mutation in Munc18-1, which enhances synaptobrevin binding, leads to a gain of function, whereas the L348R mutations, which disrupts synaptobrevin binding, impairs the function of munc18-1 in membrane fusion. The M330E mutation does not alter synaptobrevin binding or fusion.
Sitarska E, Xu J, Park S, Liu X, Quade B, Stepien K, Sugita K, Brautigam CA, Sugita S, Rizo J.
eLife 2017 May; 6: e24278.
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.
PubMed: 28477408. Doi: 10.7554/eLife.24278. free PMC article
