Purification and Characterization of a Major Cell Surface Glycoprotein in Zajdela Ascites Hepatoma Cells Which Displays a Potent Concanavalin A Receptor Activity

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Abstract
A major cell surface sialoglycoprotein with Concanavalin A receptor activity has been isolated from rat Zajdela ascites hepatoma cells. The sialic acid residues of the plasma membrane glycoproteins were specifically labeled by oxidation with NaIO4 followed by reduction with NaB3H4. Surface-labeled glycoproteins were released by short incubations with TPCK-trypsin at 37°C and then separated by gel filtration on Sepharose 6B column. The predominantly labeled fraction, GP II2, was then purified by chromatography on DEAE-cellulose equilibrated with 0.05 M phosphate buffer, pH 7.5, and eluted with increasing molarities of NaCl. It was shown to be homogeneous by protein and carbohydrate staining on SDS-polyacrylamide gels, isoelectric focusing, rechromatography on DEAE-cellulose and immunoelectrophoresis. It has an apparent molecular weight of 110,000 daltons. The location of GP II2on the cell surface was confirmed by the fact that it could be labeled metabolically with, D-(3H) glucosamine and externally through the nonpenetrating periodate-NaB3H4 system. GP II2could not be removed from the cell surface by high salt concentrations, chelator, or chaotropic agents but was released from the membrane by detergents. This suggests that GP II2could be an integral protein. Analysis of the carbohydrate composition of GP II2 revealed galactose, N-acetylglucosamine, N-acetylgalactosamine, and sialic acid as major constituents and mannose as a minor one. This suggests that it contains carbohydrate chains both O- and N-linked to the polypeptide chain, most of them being O-linked. Finally, GP II2has a potent Concanavalin A receptor activity. It inhibits the interaction between Concanavalin A and hepatoma cells and suppresses its effects on hepatoma cell proliferation.