The enhanced multivalent and superselective binding of CTB to Le x is in stark contrast to the lack of observable binding to the lactosyl glycopolymers (Figure ). Several groups have demonstrated that multivalent galactose-and lactose-based compounds can be used as inhibitors of CTB binding to GM1-coated surfaces, and lactose has been shown to bind to the E. coli heat-labile toxin GM1 binding site which is almost identical to the GM1 binding site in CTB. The affinity of CTB for simple galactosides is about 15 mM, which is only about 1.5-fold lower than its affinity for Le x . Therefore, it might have been expected that CTB would also bind to the lactosyl glycocalyx models. It may be that the mismatch in multivalent architecture for the lactosyl glycocalyx and CTB has greater impact on binding than for the Gb3 glycocalyx binding the STxB, as the latter binds with a 10-fold higher monovalent affinity.