Munc-18

Munc-18 (an acronym for mammalian uncoordinated-18) protein is the mammalian homologue of the unc-18 protein (which can be found in organisms such as the C. elegans) and is a member of the Sec1/Munc18-like (SM) protein family. Munc-18 has been identified as an essential component of the synaptic vesicle fusion protein complex and crucial for the regulated exocytosis of neurons and neuroendocrine cells.

Function
Munc-18 binds syntaxin and forms a syntaxin/munc-18 complex which is thought to precede and/or regulate the formation of vesicle priming, a process mediated by VAMP, SNAP-25 and syntaxin. Munc18-1, a member of the SM family, has multiple roles in exocytosis. It directly promotes syntaxin stability and either controls the spatially correct assembly of core complexes for SNARE-dependent fusion, or acts as a direct component of the fusion machinery through the interaction with SNARE core. Deletion of munc18-1 leads to a defect in secretory vesicle docking. Furthermore, the munc18-1 deficient mouse is the first mouse model wherein neurotransmitter secretion is completely absent. This mouse model is appropriately titled the "silent mouse."

Family members
The following is a list of human munc-18 proteins: