The Human α 2-Macroglobulin Receptor: Identification of A 420-kD Cell Surface Glycoprotein Specific for the Activated Conformation of α 2-Macroglobulin

• Published in: The Journal of cell biology 1990-04, Vol.110 (4), p.1041-1048
• Main Authors: Ashcom, James D., Tiller, Steven E., Dickerson, Kenneth, Cravens, Janet L., Argraves, W. Scott, Strickland, Dudley K.
• Format: Article
• Language: English
• Subjects: alpha-Macroglobulins - metabolism; alpha-Macroglobulins - ultrastructure; Animals; Cell Line; Chromatography; Chromatography, Affinity; Electrophoresis, Polyacrylamide Gel; Endocytosis; Female; Fibroblasts; Gels; Humans; Kinetics; Ligands; Low Density Lipoprotein Receptor-Related Protein-1; Membrane Glycoproteins - isolation & purification; Membrane Glycoproteins - metabolism; Methylamines; Molecular Weight; Molecules; Placenta - metabolism; Pregnancy; Protein Conformation; Receptors; Receptors, Immunologic - isolation & purification; Receptors, Immunologic - metabolism; Resins; Washing
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.110.4.1041

Ligand affinity chromatography was used to purify a cell surface α 2-macroglobulin (α 2 M) receptor. Detergent extracts of human placenta were applied to an affinity matrix consisting of α 2 M, previously reacted with methylamine, coupled to Sepharose. Elution with EDTA specifically released polypeptides with apparent molecular masses of 420 and 39 kD. In some preparations, small amounts of a 90-kD polypeptide were observed. The 420- and 39-kD polypeptides appear specific for the forms of α 2 M activated by reaction with proteinases or methylamine and do not bind to an affinity matrix consisting of native α 2 M coupled to Sepharose. Separation of these two polypeptides was accomplished by anion exchange chromatography, and binding activity was exclusively associated with the 420-kD polypeptide. The purified 420-kD protein binds to the conformationally altered forms of α 2 M that are known to specifically interact with α 2 M receptors and does not bind to native α 2 M. Binding of the 420-kD polypeptide to immobilized wheat germ agglutinin indicates that this polypeptide is a glycoprotein. The cell surface localization of the 420-kD glycoprotein was confirmed by affinity chromatography of extracts from surface radioiodinated fibroblasts. These properties suggest that the 420-kD polypeptide is a cell surface receptor for the activated forms of α 2 M.