Glycoprotein-concanavalin A interaction: role of protein conformation in the specific interaction of glycoprotein with concanavalin A.

The specific binding of two glycoproteins, ovomucoid and ovalbumin to concanavalin A was studied in 0.01 M Tris-HCl buffer, pH 7.4, containing 0.2 M NaCl and 1 mM each of magnesium acetate, calcium acetate and manganese chloride at 30 degrees C. Native ovalbumin was a better ligand than ovomucoid in its reaction with concanavalin A-sepharose 4B; in the inhibition of the lectin binding to dextran and cross-linked dextran, Sephadex G-150, and in the rate of precipitin reaction. Reduction of disulphide bonds of the two glycoproteins with 2-mercaptoethanol and subsequent alkylation with iodoacetate produced significant conformational change as evidenced by the increase in the hydrodynamic volume measured by intrinsic viscosity. The native and modified glycoproteins were indistinguishable in inhibiting the binding of dextran and Sephadex G-150 to the lectin, however, their pronase digest (or glycopeptides) were most effective inhibitors. Substantial (4-fold) decrease in the rate of precipitin reaction of the lectin with glycoprotein which was noted with conformationally altered glycoproteins suggested the importance of native protein conformation in the specific interaction of the two glycoproteins with concanavalin A.