LDL (Low Density Lipoprotein) receptor (LDLR) mediates the endocytosis of cholesterol-rich LDL. LDLR recognizes the apoprotein B100 which is embedded in the outer layer of the LDL particle. LDLR consist of a ligand-binding domain (LBD residues 1-292), epidermal growth factor precursor homology domain (EGFP residues 293-699), oligosaccharide-rich domain (residues 700-758), membrane-spanning domain (residues 759-781) and cytoplasmic domain (residues 782-832). LDLR LBD contains 7 ca. 40 amino acid long repeats (LB) containing 6 cysteine residues, making a calcium binding octahedral structure. LDLR EGFP contains 2 EGF repeats followed by 6 YWTD repeats and another EGF repeat. LDLR LBD residues 133-273 are named C-type lectin-like domain. LDLR sits on the cell surface and binds LDL particles which circulate in the blood stream. LDLR transports the LDL particle into the cell where the cholesterol is used. Upon release of the LDL particle, the LDLR is recycled back into the cell membrane surface.
