In-cellulo chemical cross-linking to visualize protein-protein interactions.

Reversible protein-protein interaction in cells is an integral and central aspect of intracellular signaling mechanisms. This allows distinct signaling cascades to become active upon stimulation with external signal resulting in cellular and physiological responses. Several distinct methods are currently available and utilized routinely to monitor protein-protein interactions including co-immunoprecipitation (co-IP). An inherent limitation associated with co-IP assay however is the inability to efficiently capture transient and short-lived interactions in cells. Chemical cross-linking of such transient interactions in cellular context using cell permeable reagents followed by co-IP overcomes this limitation, and allows a simplified approach without requiring any sophisticated instrumentation. In this chapter, we present a step-by-step protocol for monitoring protein-protein interaction by combining chemical cross-linking and co-immunoprecipitation using GPCR-β-arrestin complex as a case example. This protocol is based on previously validated method that can potentially be adapted to capture and visualize transient protein-protein interactions in general.