Single-residue bioorthogonal labeling of G protein-coupled receptors (GPCRs) in live cells for quantitative analysis

To perform quantitative studies of membrane bound G protein-coupled receptors (GPCRs) with high-performance microscopy, the proteins must first be labeled with bright and photostable dyes. The labeling method should be minimally invasive to avoid perturbing the GPCR function and result in quantitative yields to allow stoichiometric data analysis. For the precise quantification of dye yields, a method based on fluorescence fluctuation microscopy (molecular brightness) has been developed. The method can extract the number of labeling sites at the single-cell level. Because the reported technique is performed using a commercially available microscope, the approach can be used for the general study of membrane proteins with fluorescence microscopy.