Humans express nearly 1000 different G-protein-coupled receptors (GPCRs), which are plasma membrane-embedded signaling proteins that coordinate cell-cell interactions, protein trafficking, cellular migration, and metabolism, among other functions. When the activity of a GPCR becomes dysregulated, tumor initiation, progression, invasion, and metastasis can result. Consequently, GPCRs are critical therapeutic targets. It is estimated that one-half to one-third of all marketed drugs act through binding a GPCR. Nevertheless, there remain many GPCRs for which ligands and inhibitors have not yet been identified.
GPCRs are transmembrane proteins, which makes their isolation for use in ligand-binding assays challenging. Transmembrane proteins are difficult to solubilize, extract, and purify. When detergent is used to solubilize the GPCRs, the detergent can impair protein structure, stability, and function. The present technology is a cell-free, detergent-free platform and method that facilitates ligand-binding assays for water-soluble variants of GPCRs.