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Intracellular transport is more specialized than diffusion; it is a multifaceted process which utilizes transport vesicles. Transport vesicles are small structures within the cell consisting of a fluid enclosed by a lipid bilayer that hold cargo. These vesicles will typically execute cargo loading and vesicle budding, vesicle transport, the ...
Vesicular transport adaptor proteins are proteins involved in forming complexes that function in the trafficking of molecules from one subcellular location to another. [2] [3] [4] These complexes concentrate the correct cargo molecules in vesicles that bud or extrude off of one organelle and travel to another location, where the cargo is ...
SNARE, cargo, and other proteins are also needed for these processes to occur. Pre-budding complex (composed of Sar1-GTP and Sec23/24) recruits the flexible Sec13p/31p complex, characterized by polymerization of the Sec13/31 complex with other Sec13/31 complexes to form a cuboctahedron with a broader lattice than its Clathrin vesicle analog.
COPII coats consist of the small GTP-binding protein Sar1 and two additional complexes: Sec23/Sec24 and Sec13/Sec31. These coat proteins interact with membrane cargo proteins, ensuring that the right proteins are packaged into vesicles. The vesicles then move toward the cis-Golgi network, where they enter via COPII-mediated transport. [7] The ...
Vesicles can also fuse with other organelles within the cell. A vesicle released from the cell is known as an extracellular vesicle. Vesicles perform a variety of functions. Because it is separated from the cytosol, the inside of the vesicle can be made to be different from the cytosolic environment. For this reason, vesicles are a basic tool ...
However, several observations (described above) have now demonstrated that it is more likely that transport between these two compartments occurs by a maturation process, rather than vesicle transport. Another unique identifying feature that differs between the various classes of endosomes is the lipid composition in their membranes.
In mammalian organisms, COPII vesicles that have budded from exit sites in the endoplasmic reticulum lose their coats and fuse to form the vesicular-tubular cluster (VTC). Retrieval (or retrograde) transport in COPI vesicles returns many of the lost ER resident proteins back to the endoplasmic reticulum. Forward (or anterograde) transport moves ...
Adaptor protein (AP) complexes are found in coated vesicles and clathrin-coated pits. AP complexes connect cargo proteins and lipids to clathrin at vesicle budding sites, as well as binding accessory proteins that regulate coat assembly and disassembly (such as AP180, epsins and auxilin). There are different AP complexes in mammals.