The Low-Density Lipoprotein (LDL) Receptor, also known as LDLR, FH, FHC, or LDLCQ2, is a mosaic protein composed of approximately 840 amino acids (after signal peptide removal) that mediates the endocytosis of cholesterol-rich LDL. This cell-surface receptor recognizes apolipoprotein B100, which is embedded in the phospholipid outer layer of LDL particles, as well as apolipoprotein E found in chylomicron remnants and VLDL remnants (IDL). The LDL receptor belongs to the LDL receptor gene family.
LDL receptor complexes are located in clathrin-coated pits on the cell surface. When bound to LDL-cholesterol via adaptors, these complexes are internalized to form clathrin-coated vesicles within the cell. This process, known as endocytosis, allows for the efficient internalization of LDL-cholesterol and prevents it from diffusing across the membrane surface. This occurs in all nucleated cells, but is most prominent in the liver, which removes approximately 70% of LDL from the circulation.