User:M210956/Asialoglycoprotein receptor

The asialoglycoprotein receptor contains two subunits, asialoglycoprotein receptor 1 (ASGR1) and asialoglycoprotein receptor 2 (ASGR2). These subunits may form different quaternary forms such as dimers, trimers, tetramers to allow for specific substrate binding or endocytosis. ASGR 1 is the major subunit and has 8 exons and is roughly 6 kb in length. ASGR 2 is the minor subunit and has 9 exons and is about 13.5 kb long.

History
The asialoglycoprotein receptor was first identified in 1968 by Morell et al. and was the first mammalian lectin identified. The researchers transferred radioactively-labeled ceruloplasmin that had undergone a reaction with the enzyme neuraminidase to remove the protein's terminal sialic acid, generating an asialoglycoprotein. Upon injection of the radioactive protein into rabbits, the radioactivity of the entire asialoglycoprotein moved from the blood into the liver. This fast movement from the blood into the liver only occurred if the sialic acid of the protein was removed; i.e., if the protein had an exposed galactose residue (that would normally be covered by the sialic acid). Thus, it was concluded that a receptor is capable of recognizing asialoglycoproteins (i.e., proteins that have lost their terminal sialic acids) and removing them from circulation by transporting them to the liver.