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Exocytosis is a form of active transport and bulk transport in which a cell transports molecules out of the cell. As an active transport mechanism, exocytosis requires the use of energy to transport material. Exocytosis and its counterpart, endocytosis, are used by all cells because most chemical substances important to them are large polar molecules that cannot pass through the hydrophobic portion of the cell membrane by passive means. Exocytosis is the process by which a large amount of molecules are released; thus it is a form of bulk transport. Exocytosis occurs via secretory portals at the cell plasma membrane called porosomes. Porosomes are permanent cup-shaped lipoprotein structure at the cell plasma membrane, where secretory vesicles transiently dock and fuse to release intra-vesicular contents from the cell.
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Exocyst complex component 3 is a protein that in humans is encoded by the EXOC3 gene.
Exocyst complex component 5 is a protein that in humans is encoded by the EXOC5 gene.
Ras-related protein Rab-11B is a protein that in humans is encoded by the RAB11B gene. Rab11b is reported as most abundantly expressed in brain, heart and testes.
Autophagy-related protein 8 (Atg8) is a ubiquitin-like protein required for the formation of autophagosomal membranes. The transient conjugation of Atg8 to the autophagosomal membrane through a ubiquitin-like conjugation system is essential for autophagy in eukaryotes. Even though there are homologues in animals, this article mainly focuses on its role in lower eukaryotes such as Saccharomyces cerevisiae.
Membrane vesicle trafficking in eukaryotic animal cells involves movement of biochemical signal molecules from synthesis-and-packaging locations in the Golgi body to specific release locations on the inside of the plasma membrane of the secretory cell. It takes place in the form of Golgi membrane-bound micro-sized vesicles, termed membrane vesicles (MVs).
Rab GTPases are molecular switches that regulate membrane traffic. They are active in their GTP-bound form and inactive when bound to GDP. The GTPase YPT1, and its mammalian homologue Rab1, regulate membrane-tethering events on three different pathways: autophagy, ER-Golgi, and intra-Golgi traffic. In the yeast Saccharomyces cerevisiae, many of the ATG proteins needed for macroautophagy are shared with the biosynthetic cytoplasm to the vacuole-targeting (CVT) pathway that transports certain hydrolases into the vacuole. Both pathways require YPT1; however, only the macroautophagy pathway is conserved in higher eukaryotes. In the macroautophagy pathway, Rab1 mediates the recruitment of Atg1 to the PAS. Rab1 regulates macroautophagy by recruiting its effector, Atg1, to the PAS to tether Atg9 vesicles to each other or to other membranes.
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Exomer is a heterotetrameric protein complex similar to COPI and other adaptins. It was first described in the yeast Saccharomyces cerevisiae. Exomer is a cargo adaptor important in transporting molecules from the Golgi apparatus toward the cell membrane. The vesicles it is found on are different from COPI vesicles in that they do not appear to have a "coat" or "scaffold" around them.
References
- ↑ Saha T, Dash C, Jayabalan R, et al. (2021). "Intercellular nanotubes mediate mitochondrial trafficking between cancer and immune cells". Nat. Nanotechnol. 17 (1): 98–106. doi:10.1038/s41565-021-01000-4. PMC 10071558 . PMID 34795441.
- 1 2 3 Hsu SC, TerBush D, Abraham M, Guo W (2004). "The exocyst complex in polarized exocytosis". Int Rev Cytol. International Review of Cytology. 233: 243–65. doi:10.1016/S0074-7696(04)33006-8. ISBN 978-0-12-364637-8. PMID 15037366.
- ↑ Bowser R, Müller H, Govindan B, Novick P (September 1992). "Sec8p and Sec15p are components of a plasma membrane-associated 19.5S particle that may function downstream of Sec4p to control exocytosis". J Cell Biol. 118 (5): 1041–56. doi:10.1083/jcb.118.5.1041. PMC 2289594 . PMID 1512289.
- ↑ TerBush DR, Novick P (July 1995). "Sec6, Sec8, and Sec15 are components of a multisubunit complex which localizes to small bud tips in Saccharomyces cerevisiae". J Cell Biol. 130 (2): 299–312. doi:10.1083/jcb.130.2.299. PMC 2199927 . PMID 7615633.
- ↑ TerBush DR, Maurice T, Roth D, Novick P (December 1996). "The Exocyst is a multiprotein complex required for exocytosis in Saccharomyces cerevisiae". EMBO J. 15 (23): 6483–94. doi:10.1002/j.1460-2075.1996.tb01039.x. PMC 452473 . PMID 8978675.
