Real-time competitive kinetic analysis of interactions between low-molecular-weight ligands in solution and surface-immobilized receptors.

With surface plasmon resonance detection it is possible to measure the binding kinetics between a macromolecule in solution and a receptor immobilized on a sensor surface. The detector response is proportional to the mass of the analyte that binds to the surface, and therefore, a direct observation of a low-molecular-weight (lmw) analyte ( < 5000 Da) interacting with its immobilized binding partner is normally not possible. I describe here a competitive approach in which a lmw analyte and a high-molecular-weight analyte react at the same time with the immobilized receptor. Using this approach it is possible to extend kinetic analysis to lmw analyte-receptor interactions. A qualitative analysis allows rapid affinity ranking of different lmw analytes interacting with the same receptor, and a quantitative analysis of binding data allows the calculation of rate constants for the lmw analyte-receptor interaction. The competitive kinetics approach may therefore be used as an alternative to other affinity techniques for the characterization of lmw ligands, for identification of inhibitors, and for drug screening.