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Exosomes are formed by invagination within a cell to create an intracellular vesicle called an endosome, or an endocytic vesicle. In general, exosomes are formed by segregating the cargo (e.g., lipids, proteins, and nucleic acids) within the endosome. Once formed, the endosome combines with a structure known as a multivesicular body (MVB). The ...
Exosomes are extracellular vesicles having a unique biogenesis pathway via multivesicular bodies. Exosome formation starts with the invagination of the multi-vesicular bodies (MVBs) or late endosomes to generate intraluminal vesicles (ILVs). [58] There are various proposed mechanisms for formation of MVBs, vesicle budding, and sorting.
The process of creating vesicles within the endosome is thought to be enhanced by the peculiar lipid BMP or LBPA, which is only found in late endosomes, endolysosomes or lysosomes. [12] When the endosome has matured into a late endosome/MVB and fuses with a lysosome, the vesicles in the lumen are delivered to the lysosome lumen.
A vesicle is a relatively small, membrane-enclosed sac that stores or transports substances. [6] The cell membrane is a protective barrier that regulates what enters and leaves the cell. [ 7 ] There is also an organelle known as the Spitzenkörper that is only found in fungi, and is connected with hyphal tip growth.
EEA1 is a RAB5A effector protein which binds via an N-terminal zinc finger domain and is required for fusion of early and late endosomes and for sorting at the early endosome level. [ 5 ] [ 6 ] EEA1 plays a role in endocytosis and is recruited by Rab5-GTP to endosomal membranes. [ 7 ]
The MPR-lysosomal enzyme complex is translocated to a pre-lysosomal compartment, known as an endosome, in a COPII-coated vesicle. [11] [12] This targeting away from the secretory pathway is achieved by the presence of a specific sorting signal, an acidic cluster/dileucine motif, in the cytoplasmic tails of the MPRs. [13]
A mature pit will be cleaved from the plasma membrane through the use of membrane-binding and fission proteins such as dynamin (as well as other BAR domain proteins), [2] forming a clathrin-coated vesicle that then uncoats of clathrin and typically fuses to a sorting endosome.
The complex is then responsible for binding to a lipid on the endosomal membrane, which recruits these tagged proteins to the endosome. [7] Once properly localized , these proteins are then taken into the endosome via vesicles, forming multivesicular bodies, and are eventually delivered to the lysosome where they are degraded.