Abstract
G protein-coupled receptors (GPCRs) exhibit signaling bias, or preferential activation of heterotrimeric G proteins versus GPCR receptor kinase (GRK)-mediated β-arrestin signaling. The protease-activated receptor-1 (PAR1) GPCR activates both G protein and β-arrestin in response to thrombin, but only β-arrestin in response to activated protein C (APC). Thrombin-activated PAR1-G protein signaling is desensitized by β-arrestin-1, whereas APC-activated PAR1 signaling is propagated by β-arrestin-2. The mechanisms underlying PAR1 biased signaling are not known. Here, using computational modeling and cell biology studies, we reveal the molecular basis of signaling by thrombin- and APC-activated PAR1. Although both thrombin- and APC-induced PAR1 signaling are regulated by the same GRK isoform, GRK5, the two types of signaling are differentially dependent on GRK5 membrane anchoring, PAR1 C-terminal phosphorylation, and the binding mode of β-arrestin-2. These differences translate into distinct β-arrestin-2 conformations and define the cytoprotective signaling signature by APC which contrasts with thrombin inflammatory signaling.