Quantification of small molecule-receptor affinities and kinetics by acoustic profiling

The label-free RAPid 4 system that exploits resonant acoustic profiling (RAP) from Akubio (Cambridge, UK) was used to determine the affinity and kinetics for several different small molecule-receptor interactions. This was achieved by attaching the target receptor to the surface of quartz crystal resonators through a variety of specific coupling chemistries, followed by application of a small-molecular-weight ligand to the receptor via a microfluidic flow-based delivery system. Rank order of binding was determined for very weak interactions such as cofactor binding to glucose dehydrogenase. Moderate interaction affinities and binding kinetics could be determined for biotin binding to a specific antibody, and also for several low-molecular-weight sulfonamide analogues binding to human carbonic anhydrase isoform II. The equilibrium binding constants were in general agreement with the values obtained by kinetic analysis of the data, as well as with previously published values obtained using surface plasmon resonance, stopped flow fluorescence, and isothermal titration calorimetry.