Measuring Binding Affinity of CoV2 Spike Proteins to ACE2 Receptor Using KinExA

To infect a cell, viruses specifically interact with receptors present on the surface of target cells. Quantification of this interaction is important not only for a better understanding of infectivity or developing novel diagnosis approaches but also when screening for specific inhibitors to be used as antiviral drugs. In this respect, we describe the use of the Kinetics Exclusion Assay technology for measuring the affinity between the spike protein of the CoV-2 virus and its specific membrane receptor ACE-2. To achieve our scientific goals, we functionalized small plastic beads with the spike protein and utilized them as a solid phase to capture the free ACE-2 present in previously equilibrated solutions containing a fixed amount of ACE-2 receptor (Constant Binding Partner) and a variable amount of spike protein (Titrant). We estimated the fraction of ACE-2 captured by utilizing a biotinylated receptor, which specifically bound fluorescent streptavidin molecules used as label. Our measured binding affinity, K _d , was estimated to be 14.9 nM, which is within the range reported from utilizing different approaches. In conclusion, this approach provides an accurate estimate of the binding affinity of the spike protein to the ACE-2 receptor.