Protein unc-13 homolog D, also known as munc13-4, is a protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 that in humans is encoded by the UNC13D gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

.

Function

Munc13-4 is a member of the UNC13 family, containing similar domain structure as other family members but lacking an N-terminal phorbol

Phorbol

Phorbol is a natural, plant-derived organic compound. It is a member of the tigliane family of diterpenes. It was first isolated in 1934 as the hydrolysis product of croton oil, which is derived from the seeds of Croton tiglium. Phorbol's structure was determined in 1967...

 ester-binding C1 domain present in other Munc13 proteins. The protein appears to play a role in vesicle

Vesicle (biology)

A vesicle is a bubble of liquid within another liquid, a supramolecular assembly made up of many different molecules. More technically, a vesicle is a small membrane-enclosed sack that can store or transport substances. Vesicles can form naturally because of the properties of lipid membranes , or...

 maturation during 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...

 and is involved in regulation of cytolytic granule

Granule (cell biology)

In cell biology, a granule is a small particle. It can be any structure barely visible by light microscopy. The term is most often used to describe a secretory vesicle.-Leukocytes:...

s secretion.

Munc13-4 is an is essential protein in the intracellular trafficking

Protein targeting

Protein targeting or protein sorting is the mechanism by which a cell transports proteins to the appropriate positions in the cell or outside of it. Sorting targets can be the inner space of an organelle, any of several interior membranes, the cell's outer membrane, or its exterior via secretion...

 and exocytosis of lytic granules. It is targeted to CD63

CD63

CD63 antigen is a protein that in humans is encoded by the CD63 gene.CD63 is a good marker for flow cytometric quantification of in vitro activated basophils for diagnosis of IgE-mediated allergy. The test is commonly designated as basophil activation test -Interactions:CD63 has been shown to...

 positive secretory lysosomes. The C-terminal C2 domain of the protein is involved in this process.

Clinical significance

Mutations in the UNC13D gene are associated with hemophagocytic lymphohistiocytosis

Hemophagocytic lymphohistiocytosis

Hemophagocytic lymphohistiocytosis , also known as hemophagocytic syndrome, is an uncommon hematologic disorder that, typically, clinically manifests as fever, hepatosplenomegaly, lymphadenopathy, jaundice and rash, with laboratory findings of lymphocytosis and histiocytosis, and the pathologic...

type 3.