Applications of a catch and release electrospray ionization mass spectrometry assay for carbohydrate library screening.

Applications of a catch and release electrospray ionization mass spectrometry (CaR-ESI-MS) assay for screening carbohydrate libraries against target proteins are described. Direct ESI-MS measurements were performed on solutions containing a target protein (a single chain antibody, an antigen binding fragment, or a fragment of a bacterial toxin) and a library of carbohydrates containing multiple specific ligands with affinities in the 103 to 106 M–1 range. Ligands with moderate affinity (104 to 106 M–1) were successfully detected from mixtures containing >200 carbohydrates (at concentrations as low as 0.25 μM each). Additionally, the absolute affinities were estimated from the abundance of free and ligand-bound protein ions determined from the ESI mass spectrum. Multiple low affinity ligands (∼103 M–1) were successfully detected in mixtures containing >20 carbohydrates (at concentrations of ∼10 μM each). However, identification of specific interactions required the use of the reference protein method to co...