Use of a biosensor to determine the binding kinetics of five lectins for Galactosyl-N-acetylgalactosamine

The dietary lectins, edible mushroom (ABL) and Jacalin (JAC) inhibit the proliferation of colonic cancer cells, whereas Amaranth (ACL) and peanut (PNA) stimulate their proliferation. All these lectins share as their preferred ligand the Thomsen-Friedenreich (TF) antigen galactosyl 1,3 N-Acetylgalactosamine (Gal1,3GalNAc), but differ in their finer specificities for modifications of this determinant and in their specificities for cancerous epithelia. We have investigated, using a resonant mirror biosensor, the kinetics of binding of these lectins, and Maclura pomifera lectin (MPL), which is similar to JAC, to two different Gal-GalNac bearing glycoproteins, antarctic fish antifreeze glycoprotein (AFG) and asialofetuin. JAC had the highest affinity for AFG [K_d 0.027 M] due to a fast association rate constant [k_ass 610,000 (Ms)^–1]. The other lectins had considerably lower affinities, with K_d ranging from 0.16 M (ABL) to 5.7 M (PNA), largely due to slower k_ass [ABL 74,000 (Ms)^–1 to PNA 2700 (Ms)^–1]. Similarly, JAC had a much higher affinity for asialofetuin [K_d 0.083 M] than the other lectins [K_d 1.0 M–4.5 M]. Affinities were also calculated from the extent of binding at equlibrium and were generally similar to those calculated from the kinetic parameters indicating the true nature of these values.