LIGAND-INDUCED ENDOCYTOSIS OF THE ASIALOGLYCOPROTEIN RECEPTOR - EVIDENCE FOR HETEROGENEITY IN SUBUNIT OLIGOMERIZATION

The hepatic asialoglycoprotein receptor, a noncovalent hetero-oligomer of two subunits, is a constitutively cycling endocytic receptor. Howe ver, the ligand asialoorosomucoid caused downregulation of up to 40% o f surface binding sites and a twofold increase in internalization rate . This was not the result of receptor crosslinking, since monovalent l igands had the same effect. Ligand binding thus appears to transmit a signal to the cytosolic portion of the receptor not unlike in signalin g receptors, The two subunits mere endocytosed at different average ra tes lower than that of ligand, indicating heterogeneity in oligomer fo rmation and potentially in ligand specificity. (C) 1998 Federation of European Biochemical Societies.