Characterisation of a fusion event from the endocytic pathway
Endocytosis is the process by which cells internalise extracellular ligands by enclosing them within inward foldings of the plasma membrane that seal to form intracellular vesicles (Silverstein et al., 1977). Many of the ligands are selectively concentrated for uptake by first binding to specific receptors at the plasma membrane, a process known as receptor-mediated endocytosis. The receptor-bound ligands become clustered in specialised regions of the cell surface known as coated pits (Bretscher and Pearse, 1984). These pits pinch off into the cell and the resulting vesicle uncoats and fuses with a larger prelysosomal vesicle called the endosome (Helenius et al., 1983). The acidic environment within this compartment causes the ligand to dissociate from its receptor and whilst the receptor is recycled back to the plasma membrane the ligand is delivered to lysosomes where it is degraded.
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