Conformational changes in the chicken receptor for endocytosis of glycoproteins. Modulation of ligand-binding activity by Ca2+ and pH.
Limited proteolysis, gel filtration, and circular dichroism have been used to identify at least three distinct conformational states of a proteolytic fragment containing the ligand-binding domain of the chicken receptor for endocytosis of glycoproteins. Differences in the ligand-binding activity of intact receptor brought about by changing Ca2+ concentrations and pH values can be correlated with different physical states of the binding domain present under similar conditions. An active, ligand-binding state can be detected at either pH 7.8 or 5.4, but 10-fold higher concentrations of Ca2+ are required to stabilize this state at the lower pH. In all cases, the dependence on Ca2+ concentration is second-order, suggesting that two Ca2+ ions are bound to each domain. These studies demonstrate an interdependence between the effects of Ca2+ concentration and pH on both ligand-binding activity and receptor conformation, which is important to consider when describing the binding and dissociation of ligand during endocytosis.
Loeb
J A
JA
Department of Biochemistry and Molecular Biology, University of Chicago, Illinois 60637.
Drickamer
K
K
D000117:Acetylglucosamine / Q000378:metabolism; D000818:Animals; D037263:Asialoglycoprotein Receptor; D002118:Calcium / Q000494:pharmacology*; D002413:Cations, Divalent; D002850:Chromatography, Gel; D002942:Circular Dichroism; D004705:Endocytosis; D006023:Glycoproteins / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009961:Orosomucoid / Q000031:analogs & derivatives / Q000378:metabolism; D010447:Peptide Hydrolases / Q000378:metabolism; D011487:Protein Conformation; D011971:Receptors, Immunologic / Q000187:drug effects / Q000378:metabolism*
D037263:Asialoglycoprotein Receptor; D002413:Cations, Divalent; D006023:Glycoproteins; D009961:Orosomucoid; D011971:Receptors, Immunologic; C018203:agalacto-orosomucoid; D010447:Peptide Hydrolases; D002118:Calcium; D000117:Acetylglucosamine