A general framework for development and data analysis of competitive high-throughput screens for small-molecule inhibitors of protein-protein interactions by fluorescence polarization.

Equilibrium binding experiments are widely used for the accurate characterization of binding and competitive binding behavior in biological systems. Modern high-throughput discovery efforts in chemical biology rely heavily upon this principle. Here, we derive exact analytical expressions for general competitive binding models which can also explain a commonly encountered phenomenon in these types of experiments, anticooperative incomplete displacement. We explore the effects of nonspecific binding behavior and parameter misestimation. All expressions are derived in terms of total concentrations determined a priori. We discuss a general framework for high-throughput screening assays based on fluorescence polarization and strategies for assay development, sensitivity regimes, data quality control, analysis, and ranking. Theoretical findings are visualized by simulations using realistic parameter sets. Our results are the basis for the discovery of small-molecule inhibitors of the protein-protein interaction between human calcineurin and NFAT transcription factors, as discussed in the subsequent paper (31).