Surface Plasmon Resonance Imaging Measurements of the Inhibition of Shiga-like Toxin by Synthetic Multivalent Inhibitors

A variety of new methodologies to pattern biomolecules on surfaces and to detect binding events are currently being developed for high-throughput assay applications. Carbohydrates serve as attachment sites for toxins, bacteria, and viruses. Immobilized carbohydrate units can thus be used to directly detect these agents or as a platform for inhibitor assessment. In this work, modified glycosides were patterned on gold surfaces to monitor the binding of the homopentameric B<sub>5</sub> cell-recognition subunit of the Shiga-like toxin (SLT). Binding was detected with the label-free method of surface plasmon resonance (SPR) imaging. Two synthetic multivalent inhibitors were used in order to effect inhibitory binding, and SPR imaging is presented as a simple alternative to ELISA for the study of toxin inhibition. In contrast to existing methods for the study of carbohydrate−protein interactions, in particular ELISA, the use of micropatterned sensor surfaces is shown to be advantageous due to a decrease in complications and manual labor from numerous blocking, washing, and labeling steps. Carbohydrate receptor density on the sensor surface was optimized in order to effect the maximum binding of the SLT. The IC<sub>50</sub> values determined were in the low-nanomolar range for each of the two inhibitors studied.