Munc-18 protein is the mammalian homologue of the unc-18 protein (which can be found in organisms such as the C. elegans

Caenorhabditis elegans

Caenorhabditis elegans is a free-living, transparent nematode , about 1 mm in length, which lives in temperate soil environments. Research into the molecular and developmental biology of C. elegans was begun in 1974 by Sydney Brenner and it has since been used extensively as a model...

) 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

Exocytosis

Exocytosis , also known as 'The peni-cytosis', is the durable process by which a cell directs the contents of secretory vesicles out of the cell membrane...

 of neuron

Neuron

A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...

s and neuroendocrine cell

Neuroendocrine cell

Neuroendocrine cells are cells that receive neuronal input and, as a consequence of this input, release message molecules to the blood. In this way they bring about an integration between the nervous system and the endocrine system, a process known as neuroendocrine integration...

s.

Function

Munc-18 binds syntaxin

Syntaxin

Syntaxins are a family of membrane integrated Q-SNARE proteins participating in exocytosis.- Domains :Syntaxins possess a single C-terminal transmembrane domain, a SNARE domain , and an N-terminal regulatory domain ....

 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

SNAP-25

Synaptosomal-associated protein 25 is a protein that in humans is encoded by the SNAP25 gene. The SNAP-25 protein is a component of the SNARE complex, which is proposed to account for the specificity of membrane fusion and to directly execute fusion by forming a tight complex that brings the...

 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:

protein	gene
	symbol	name
MUNC18-1	STXBP1 STXBP1 Syntaxin-binding protein 1 is a protein that in humans is encoded by the STXBP1 gene.In melanocytic cells STXBP1 gene expression may be regulated by MITF.-Interactions:STXBP1 has been shown to interact with STX2, STX4 and STX1A.-Further reading:...	syntaxin binding protein 1
MUNC18-2	STXBP2 Syntaxin binding protein 2 Syntaxin-binding protein 2 is a protein that in humans is encoded by the STXBP2 gene.-Further reading:...	syntaxin binding protein 2
MUNC18-3	STXBP3 Syntaxin binding protein 3 Syntaxin-binding protein 3 is a protein that in humans is encoded by the STXBP3 gene.-Interactions:Syntaxin binding protein 3 has been shown to interact with STX2 and STX4.-Further reading:...	syntaxin binding protein 3
MUNC18-4	STXBP4	syntaxin binding protein 4
MUNC18-5	STXBP5 STXBP5 Syntaxin-binding protein 5 is a protein that in humans is encoded by the STXBP5 gene.-Interactions:STXBP5 has been shown to interact with STX4 and STX1A.-Further reading:...	syntaxin binding protein 5
MUNC18-6	STXBP6	syntaxin binding protein 6