Screening oligosaccharide libraries against lectins using the proxy protein electrospray ionization mass spectrometry assay

An electrospray ionization mass spectrometry (ESI-MS) assay for screening carbohydrate libraries against lectins is described. The assay is based on the proxy protein ESI-MS method, which combines direct ESI-MS protein–ligand binding measurements and competitive protein binding, to simultaneously detect and quantify protein–carbohydrate interactions. Specific interactions between components of the library and the target protein (PT) are identified from changes in the relative abundances (as measured by ESI-MS) of the carbohydrate complexes of a proxy protein (Pproxy), which binds to all components of the library with known affinity, upon addition of PT to the solution. The magnitude of the change in relative abundance of a given Pproxy–ligand complex provides a quantitative measure of the affinity of the corresponding PT–ligand interaction. A mathematical framework for the implementation of the method in the case of monovalent (single binding site) Pproxy and monovalent and multivalent (multiple equivalen...