The interaction between wheat germ agglutinin and membrane incorporated glycophorin A. An optical binding study

Abstract
A novel integrated optical technique is used to monitor the kinetics of incorporation of glycophorin A (GPA) from solution into a planar dimyristoylphosphatidylcholine-cholesterol bilayer membrane, and the subsequent binding of wheat germ agglutinin (WGA) to the membrane-incorporated GPA. The technique significantly improves the attainable accuracy of kinetic measurements. The number of bound molecules can be determined to a precision of ca ± 80 mol µm−2. Our results show that GPA incorporates spontaneously into the bilayer. Binding of WGA to GPA is optimal in the presence of human serum albumin, and can be reversed byN-acetyl-d-glucosamine. The kinetics of the binding are consistent with the presence of two classes of kinetically distinguishable binding sites with association rates of 2.0×104 and 9.6×102 M−1 s−1, and dissociation rates of 2.7×10−3 s−1 and −5 s−1, respectively. A stoichiometry of 4 WGA monomers per GPA monomer was determined as characteristic of the overall binding interaction.