The low-density lipoprotein receptor (LDL-R) is a mosaic protein of 839 amino acids (after removal of 21-amino acid signal peptide) that mediates the endocytosis of cholesterol-rich low-density lipoprotein (LDL). It is a cell-surface receptor that recognizes apolipoprotein B100 (ApoB100), which is embedded in the outer phospholipid layer of very low-density lipoprotein (VLDL), their remnants—i.e. intermediate-density lipoprotein (IDL), and LDL particles. The receptor also recognizes apolipoprotein E (ApoE) which is found in chylomicron remnants and IDL. In humans, the LDL receptor protein is encoded by the LDLR gene on chromosome 19. It belongs to the low density lipoprotein receptor gene family. It is most significantly expressed in bronchial epithelial cells and adrenal gland and cortex tissue.
Michael S. Brown and Joseph L. Goldstein were awarded the 1985 Nobel Prize in Physiology or Medicine for their identification of LDL-R and its relation to cholesterol metabolism and familial hypercholesterolemia. Disruption of LDL-R can lead to higher LDL-cholesterol as well as increasing the risk of related diseases. Individuals with disruptive mutations (defined as nonsense, splice site, or indel frameshift) in LDLR have an average LDL-cholesterol of 279 mg/dL, compared with 135 mg/dL for individuals with neither disruptive nor deleterious mutations. Disruptive mutations were 13 times more common in individuals with early-onset myocardial infarction or coronary artery disease than in individuals without either disease.