Differential association modes of the thrombin receptor PAR1 with Gαi1, Gα12, and β-arrestin 1

Although many G protein-coupled receptors (GPCRs) are known to activate multiple signaling pathways by coupling to different types of G proteins or by promoting G protein-independent events, how this occurs remains unclear. Using bioluminescence resonance energy transfer and time-resolved fluorescence resonance energy transfer, we provide evidence for protease-activated receptor 1 (PAR(1)) forming preassembled complexes with G alpha i1 but not G alpha 12. PAR(1) activation appears to rapidly induce transient G alpha i1 activation (t(1/2) = 4.13 s) but late and stable recruitment of G alpha 12 (t(1/2) = 8.8 min) in parallel with beta-arrestin 1 (t(1/2) = 7.5 min). However, there is no significant difference in the potency of the agonist-dependent response between G alpha i1, G alpha 12, and beta-arrestin 1 (EC50 values 0.48, 0.30, and 0.15 nM, respectively). Although it seems beta-arrestin 1 is recruited to preassembled PAR(1)-G alpha i1 complexes, this appears unlikely with G alpha 12, suggesting 2 distinct receptor populations. Of note, we observed a different G alpha 12 association mode with other GPCRs, indicating that preassembly and association dynamics may be specific properties of a receptor-G protein pair. Furthermore, the G alpha C terminus appears to play different roles in the distinct association modes. Consequently, G protein preassembly or recruitment may constitute novel mechanisms for controlling the kinetics and multitude of GPCR signaling pathways.-Ayoub, M. A., Trinquet, E., Pfleger K. D. G., Pin, J.-P. Differential association modes of the thrombin receptor PAR(1) with G alpha i1, G alpha 12, and beta-arrestin 1. FASEB J. 24, 3522-3535 (2010). www.fasebj.org