LDL receptor
The LDLR regulates cholesterol homeostasis in mammalian cells. LDLR binds cholesterol-carrying LDL, associates with clathrin-coated pits, and is internalized into acidic endosomes where it separates from its ligand. The ligand is degraded in lysosomes, while the receptor returns to the cell surface. The LDLR has several domains. The ligand-binding domain contains seven LDL receptor class A repeats, each with three disulphide bonds and a coordinated Ca2+ ion. The second conserved region contains two EGF repeats, followed by six YWTD or LDL receptor class B repeats and another EGF repeat. This conserved region is critical for ligand release and recycling of the receptor.