An intrabody sensor to monitor conformational activation of ss-arrestins

Agonist-induced interaction of ss- arrestins with GPCRs is critically involved in downstream signaling and regulation. This interaction is associated with activation and major conformational changes in ss- arrestins. Although there are some assays available to monitor the conformational changes in ss- arrestins in cellular context, additional sensors to report ss- arrestin activation, preferably with high-throughput capability, are likely to be useful considering the structural and functional diversity in GPCR-ss-arrestin complexes. We have recently developed an intrabody-based sensor as an integrated approach to monitor GPCR-ss-arrestin interaction and conformational change, and generated a luminescence-based reporter using NanoBiT complementation technology. This sensor is derived from a synthetic antibody fragment referred to as Fab30 that selectively recognizes activated and receptor-bound conformation of ss- arrestin1. Here, we present a step-by-step protocol to employ this intrabody sensor to measure the interaction and conformational activation of ss- arrestin1 upon agonist-stimulation of a prototypical GPCR, the complement C5a receptor (C5aR1). This protocol is potentially applicable to other GPCRs and may also be leveraged to deduce qualitative differences in ss- arrestin1 conformations induced by different ligands and receptor mutants.