Exocyst

The exocyst is an octameric protein complex involved in vesicle trafficking, specifically the tethering and spatial targeting of post-Golgi vesicles to the plasma membrane prior to vesicle fusion. It is implicated in a number of cell processes, including exocytosis, cell migration, and growth.

Subunits

The exocyst is composed of eight subunits, whose nomenclature differs between mammalian cells and Saccharomyces cerevisiae.

Subunit Mammalian cells Saccharomyces cerevisiae
1 EXOC1 Sec3
2 EXOC2 Sec5
3 EXOC3 Sec6
4 EXOC4 Sec8
5 EXOC5 Sec10
6 EXOC6 Sec15
7 EXOC7 Exo70
8 EXOC8 Exo84

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. Because of this function, the exocyst complex is heavily involved in exocytosis. Sec3 (EXOC1) and Exo70 (EXOC7) are localized to the plasma membrane, and are physically attached to the membrane by Rho GTPases 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 interactions to facilitate fusion.

The exocyst also interacts with Rho GTPases responsible for controlling cell polarity and the activity of the cytoskeleton.

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See also


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