Construction of a bioluminescence-based assay for bitter taste receptors (TAS2Rs)

In humans, a family of 25 bitter taste receptors (TAS2Rs) mediates bitter taste perception. A common approach to characterize bitter causative agents involves expressing TAS2Rs and the appropriate signal transducers in heterologous cell systems, and monitoring changes in the intracellular free calcium levels upon ligand exposure using a fluorescence-based modality. However, a fluorescence-based assay typically suffers from a low signal window, and is susceptible to interference by autofluorescence, therefore limiting its application to screening of plant or food extracts, which are likely to contain autofluorescent compounds. Here, we report the development and validation of a bioluminescence-based intracellular calcium release assay for TAS2Rs that has a better assay performance than a fluorescence-based assay. Furthermore, the bioluminescence-based assay enables the evaluation of TAS2R agonists within an autofluorescent matrix, highlighting its potential utility in the assessment of the bitterness-inducing properties of plant or food fractions by the food industry. Additionally, further improvement to the bioluminescence-based assay for some TAS2Rs was achieved by altering their N-terminal signal sequences, leading to signal window enhancement. Altogether, the bioluminescence-based TAS2R assay can be used to perform functional studies of TAS2Rs, evaluate TAS2R-modulating properties of autofluorescent samples, and facilitate the discovery of compounds that can function as promising bitter taste modulators.