GPCR Assay and Profiling Services

LinkLight is the engineered cell line technology behind most of our GPCR catalog. Each cell line expresses a TEV-tagged receptor and a luciferase-tagged β-arrestin or 14-3-3 partner. The luciferase reporter is only used for recruitment assays. The tagged receptor couples to endogenous G proteins, so cAMP and calcium assays run on the same cells without the reporter.

Choice depends on receptor coupling. cAMP assays measure Gs activation and Gi inhibition. IP1 and calcium flux both measure Gq activity: calcium flux captures a rapid kinetic response suited to screening, while IP1 accumulates over time and provides a stable endpoint suited to inverse agonist and constitutive activity studies.

Second messenger assays capture immediate G-protein activation but not the regulatory events that control signal duration and receptor internalization. Biased ligands may show little second messenger activity while strongly recruiting β-arrestin, or the reverse. Second messenger assays can also respond to endogenous receptors in the host cell, while LinkLight recruitment signal requires the tagged receptor.  

Ligand bias describes a compound that preferentially activates one signaling pathway over another at the same receptor. It is measured by generating concentration-response curves for a G-protein readout and a β-arrestin readout, then comparing potency and efficacy relative to a reference agonist. Running both assays in the same cell line removes cell-background variables from the comparison.  

Binding assays measure whether and how strongly a compound occupies the receptor, independent of downstream response. Functional assays measure the cellular consequence of binding, distinguishing agonists, antagonists, inverse agonists, and allosteric modulators. Programs typically use binding for affinity and selectivity, and functional assays for mechanism and efficacy. 

Yes. β-arrestin recruitment is independent of G-protein coupling, providing a readout for orphan receptors with unknown coupling. The catalog includes multiple orphan receptors, and parallel second messenger assays can be used to assign coupling once activity is detected.

Yes. cAMP, IP1, and LinkLight assays use homogeneous plate-based formats with standard luminescent or TR-FRET detection, and calcium flux runs in kinetic mode on the FLIPR Penta platform. LinkLight uses economical reagents and a simple luminescent readout, making it cost-effective for large-scale screening.

Yes. Our GPCR team scopes the project with you, acquires or generates a suitable cell line, and qualifies the assay to catalog standards. Custom LinkLight cell lines can be built for β-arrestin, 14-3-3, or other protein interaction partners.