Localization of Cathepsin D in Endosomes: Characterization and Biological Importance
Proteases were initially identified in endosomes through studies of receptor-ligand transport.1 During receptor-mediated endocytosis, cell surface receptors bind exogenous ligands (Figure 1). These receptor-ligand complexes are internalized by clathrin-coated vesicles, which give rise to endosomes. Shortly after endosome formation, the internal pH of these vesicles drops to between pH 5–6.2 Many internalized receptor-ligand complexes dissociate upon endosome acidification, with the released receptors recycling back to the cell surface. Ligands delivered into endosomes undergo a variety of fates including transport back to the cell surface3 or sorting to different intracellular compartments such as lysosomes and the Golgi.4,5 Susceptible protein ligands are cleaved in endosomes indicating that these vesicles also serve as a processing compartment.1,6,8
KeywordsCysteine Protease Lysosomal Enzyme Antigen Processing Aspartic Protease Endosome Acidification
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