Binding of Transferrin to the Core Protein of Fibroblast Proteoheparan Sulfate

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 81; no. 18; pp. 5657 - 5661
• Main Authors: Fransson, Lars-Ake, Carlstedt, Ingemar, Coster, Lars, Malmstrom, Anders
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 01-09-1984; National Acad Sciences
• Subjects: Animal cells; Blood Proteins - metabolism; Cells, Cultured; Chlorides; Embryo, Mammalian; Female; Fibroblasts; Fibroblasts - metabolism; Heparan sulfate proteoglycans; Humans; Hydrogen-Ion Concentration; Kinetics; man; Molecular Weight; Monoclonal antibodies; Pregnancy; Protein Binding; Proteoglycans; proteoheparan sulfate; Receptors; Receptors, Cell Surface - metabolism; Receptors, Transferrin; skin; Skin - metabolism; Sulfates; transferrin; Transferrin - metabolism; Transferrin receptors; Transferrins
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.81.18.5657

Cell-surface-associated proteoheparan sulfate from confluent human skin fibroblasts appears to consist of two disulfide-bonded polypeptides of Mr≈ 90,000. The transferrin receptor, a ubiquitous cell-surface component of proliferating cells, also consists of two subunits of Mr90,000 linked by S--S bonds. Radiolabeled proteoheparan sulfate mixed with holotransferrin or apotransferrin at pH 4-5 followed by rabbit anti-human transferrin was adsorbed onto protein A-Sepharose to ≈ 80-90%. At pH 7.5 apotransferrin bound ≈ 40% of the proteoglycan, whereas ≈ 80% was bound to holotransferrin. Trypsin digestion of the proteoglycan markedly lowered its ability to bind transferrin. However, binding was essentially unaffected by heparan-sulfate lyase treatment and after reduction and alkylation. Over 90% of the3H activity of an L-[3H]leucine-labeled proteoglycan was recovered by immunoprecipitation (transferrin-antitransferrin) of a heparan-sulfate lyase digest of the proteoglycan. The immunoprecipitated core protein had an apparent Mrof 150,000 before reduction and Mrof 90,000 after reduction of disulfide bonds. The core protein of the proteoglycan was recognized by the monoclonal antibody B3/25, which is known to be receptor specific. The present findings suggest that the core polypeptides of proteoheparan sulfate and the transferrin receptor may be identical or closely similar.