Fluorescence polarization assays to study carbohydrate-protein interactions

Fluorescence polarization (FP) is a useful technique to study the interactions between carbohydrates and proteins in solution, by using standard equipment and minimal sample consumption. Here, we will review the most recent FP-based approaches in this field, including the study of carbohydrate-lectin, carbohydrate-enzyme and glycosaminoglycan-protein interactions. Advantages and limitations of this methodology will be discussed. To develop a FP procedure for studying carbohydrate-protein interactions, the main requirement is the design and synthesis of a suitable fluorescent glycan probe showing high affinity for the protein of interest. Different synthetic strategies employed for this purpose will be described, including the conjugation of 2-aminoethyl glycosides with amine-reactive fluorescein derivatives, the cycloaddition reaction between azido-functionalized saccharides and alkynylated fluorescent derivatives, and the reaction of the reducing end aldehyde group of an oligosaccharide with a hydrazide-containing fluorescein molecule. Competition FP experiments are particularly interesting because they enable the rapid screening of hundreds/thousands of non-labelled compounds for the discovery of molecules that block carbohydrate-protein binding, potentially modulating the subsequent biological processes.