Final answer:
Uncoating in the endosome is triggered by ATP hydrolysis, which leads to the disassembly of the clathrin coat and allows the internalized vesicle to fuse with an early endosome.
Step-by-step explanation:
Uncoating in the endosome is a crucial step in the process of receptor-mediated endocytosis. After the clathrin-coated vesicle is internalized into the cell, it loses its coat, which is composed of clathrin and associated adaptor proteins, such as adaptor protein 1 (AP1). This facilitates the fusion of the uncoated vesicle with an early endosome, forming a sorting vesicle (late endosome).
Subsequently, sorting vesicles separate imported content from the receptors, the latter being recycled back to the membrane. Eventually, a lysosome, carrying digestive enzymes, merges with the vesicle for the hydrolysis of vesicle contents, and the processed molecules are then released for cellular use. An important factor in triggering uncoating is the hydrolysis of ATP, which provides the necessary energy for the rearrangement and disassembly of the coat proteins.