What is endosome maturation?
Endosome maturation involves a conversion from Rab5 to Rab7 (Rink et al, 2005; Vonderheit and Helenius, 2005; Poteryaev et al, 2010). The conversion can be blocked by expressing a constitutively active mutant of Rab5 (Q79L), and by depletion of VPS39, a subunit of the HOPS complex (Rink et al, 2005).
How does an endosome mature?
Once endocytic vesicles have uncoated, they fuse with early endosomes. Early endosomes then mature into late endosomes before fusing with lysosomes. Early endosomes mature in several ways to form late endosomes. They become increasingly acidic mainly through the activity of the V-ATPase.
Do rabs change during endosome maturation?
During endosome maturation, Rab5 is replaced by Rab7 in a highly coordinated process referred to as Rab conversion. In this well-characterized process, Rab5 together with PtdIns3P recruits a complex containing the proteins Mon1/SAND1 and Ccz1/CCZ1 to early endosomes.
What happens in an endosome?
Endosomes are primarily intracellular sorting organelles. They regulate trafficking of proteins and lipids among other subcellular compartments of the secretory and endocytic pathway, specifically the plasma membrane Golgi, trans-Golgi network (TGN), and vacuoles/lysosomes.
Does an endosome become a lysosome?
Transport vesicles that carry lysosomal hydrolases from the trans-Golgi network (TGN) then fuse with late endosomes, leading to maturation of late endosomes into lysosomes. Inside lysosomes, acid hydrolases catalyze the degradation of internalized substances.
Is endosome a vesicle?
Endosomes are membrane-bound vesicles, formed via a complex family of processes collectively known as endocytosis, and found in the cytoplasm of virtually every animal cell. The basic mechanism of endocytosis is the reverse of what occurs during exocytosis or cellular secretion.
What is RAB5A?
Function. RAB5A localizes to early endosomes where it is involved in the recruitment of RAB7A and the maturation of these compartments to late endosomes. It drives the maturation of endosomes by transporting vacuolar (H+)-ATPases (V-ATPases) from trans-Golgi network to endocytic vesicles.
Are endosomes membrane-bound?
Endosomes are distinct membrane-bound endocytic organelles inside cells. Classically, receptors and their ligands are taken up into clathrin-coated vesicles from the plasma membrane surface during endocytosis. They are sorted to the early endosome and then targeted to various intracellular destinations.
What is the function of the early endosome?
The early endosome receives all manner of incoming material from the plasma membrane, as well as from the Golgi, and serves as an initial sorting nexus routing molecules back to the cell surface through recycling endosomes, to the trans-Golgi network by retrograde transport, or on to the late endosome/lysosome.
How is the endosome system similar to autophagy?
In the view of its parallels with autophagy in this review, the endosome system functions in importing nutrients and macromolecules into the cell from outside, and acts as a companion route as a complement to autophagy (operating with intracellular material) to provide amino acids and other degraded basic components for use by the cell.
What is the role of RAB7 in the maturation of endosomes?
One of the most substantial molecules in the maturation of autophagosomes/endosomes is Rab7, a member of small GTPases. Rab7 designates the maturation of endosomes and also autophagosomes, directing the trafficking of cargos along microtubules, and finally, participating in the fusion step with lysosomes.
How are vacuolar regions related to the endosomal system?
Vacuolar regions containing intralumenal vesicles (ILVs) detach, or mature, from early endosomes and become free MVBs (multivesicular bodies) or ECVs (endosomal carrier vesicles) ( Fig. 1 ), which eventually fuse with the late endosomes (LEs). LEs serve as a second trafficking hub and sorting station in the endosomal system.