The exocyst is an

octamer In chemistry and biochemistry, an oligomer () is a molecule that consists of a few repeating units which could be derived, actually or conceptually, from smaller molecules, monomers.Quote: ''Oligomer molecule: A molecule of intermediate relative ...

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

complex involved in

vesicle Vesicle may refer to: ; In cellular biology or chemistry * Vesicle (biology and chemistry), a supramolecular assembly of lipid molecules, like a cell membrane * Synaptic vesicle ; In human embryology * Vesicle (embryology), bulge-like features o ...

trafficking, specifically the tethering and spatial targeting of post- Golgi vesicles to the

plasma membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...

prior to vesicle fusion. It is implicated in a number of cell processes, including

exocytosis Exocytosis () is a form of active transport and bulk transport in which a cell transports molecules (e.g., neurotransmitters and proteins) out of the cell ('' exo-'' + ''cytosis''). As an active transport mechanism, exocytosis requires the use o ...

cell migration Cell migration is a central process in the development and maintenance of multicellular organisms. Tissue formation during embryonic development, wound healing and immune responses all require the orchestrated movement of cells in particular dire ...

, and growth.

Subunits

The exocyst is composed of eight subunits, whose

nomenclature Nomenclature (, ) is a system of names or terms, or the rules for forming these terms in a particular field of arts or sciences. The principles of naming vary from the relatively informal naming conventions, conventions of everyday speech to the i ...

differs between mammalian cells and ''

Saccharomyces cerevisiae ''Saccharomyces cerevisiae'' () (brewer's yeast or baker's yeast) is a species of yeast (single-celled fungus microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have been o ...

''.

Function

The exocyst complex serves to direct vesicles after the Golgi complex to specific locations on the plasma membrane and to mediate their tethering and localization to the membrane immediately before fusion. The exocyst complex has also been implicated in the active trafficking of mitochondria from immune cells to cancer cells. Because of this function, the exocyst complex is heavily involved in

. Sec3 (EXOC1) and Exo70 (EXOC7) are localized to the plasma membrane, and are physically attached to the membrane by

Rho GTPases Rho GTPase may refer to: *Any member of the Rho family of GTPases *The members of the Rho family of GTPases belonging to the '' Rho subclass'' *RHOA Transforming protein RhoA, also known as Ras homolog family member A (RhoA), is a small GTPase p ...

such as CDC42. Other complementary exocyst components such as Sec15 (EXOC6) and Sec4 are localized to the vesicle membrane. Exocyst proteins on the plasma membrane bind vesicular exocyst proteins, bringing the vesicle very close to the plasma membrane in a fashion similar to the

SNARE SNARE proteins – " SNAP REceptor" – are a large protein family consisting of at least 24 members in yeasts, more than 60 members in mammalian cells, and some numbers in plants. The primary role of SNARE proteins is to mediate vesicle fu ...

interactions to facilitate fusion. The exocyst also interacts with Rho GTPases responsible for controlling cell polarity and the activity of the

cytoskeleton The cytoskeleton is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including those of bacteria and archaea. In eukaryotes, it extends from the cell nucleus to the cell membrane and is compos ...

History

Hints of a multi-subunit complex involved in yeast exocytosis came from work in

Peter Novick Peter Novick (July 26, 1934, Jersey City – February 17, 2012, Chicago) was an American historian who was Professor of History at the University of Chicago. He was best known for writing ''That Noble Dream: The "Objectivity Question" and t ...

's group, then at Yale University School of Medicine, in the early 1990s. Works led by Robert Bowser and Daniel TerBush in 1992 and 1995 respectively isolated Sec6p and Sec8p, showing them to participate in a complex of at least eight proteins, found at the site of active exocytosis. In 1996, the same group identified the exocyst member proteins in yeast and coined the name "exocyst" for the complex.

References

External links

*https://web.archive.org/web/20051224051252/http://www.umassmed.edu/faculty/graphics/208/munson-figure-1.jpg *http://www.jbc.org/cgi/content/full/279/41/43027 Protein complexes {{protein-stub