The LDL receptor

The LDL receptor is a cell surface receptor for
low-density lipoprotein (LDL), which contains
apoB-100, the protein that carries most of the
cholesterol ester in human plasma. This receptor
mediates endocytosis of the extracellular
ligand. The LDL receptor is a membrane-bound
protein of 839 amino acids with five domains:
three extracellular domains, one transmembrane
domain, and one intracellular, with the
carboxyl end. The extracellular domains consist
of one domain with seven cysteine-rich units of
40 amino acids each, the ligand-binding region;
a domain with epidermal growth factor (EGF)
precursor homology; and a small serine- und
threonine-rich domain linked to oligosaccharides.
The transmembrane domain contains
22 hydrophobic amino acids. The fifth domain
with the intracellular COOH terminus consists
of 50 amino acids. It controls the interaction of
the receptorwith the coated pit during endocytosis.
The corresponding gene consists of 18
exons that span 45 kb genomic DNA on human
chromosome 19p13.1–13.3. In addition to the
main locus on 19p, two additional loci for autosomal
dominant hypercholesterolemia exist