Systematic identification of p11 as a signaling modulator across the GPCRome.

The microprotein p11 (S100A10) is a ubiquitously expressed molecular scaffold that is known to be required for behavioral responses to certain antidepressants, presumably through its effect on G protein-coupled receptor (GPCR)-mediated signaling. Here, we demonstrate that p11 recruitment to GPCRs is promoted by an active receptor conformation. Furthermore, by mapping the GPCR-p11 interactome using a multiplexed suspension bead array (SBA) of 211 receptors, we identified more than two dozen high-confidence physical interactors across diverse GPCR signaling families. We define the functional significance of these interactions by focusing on a novel SBA screening hit, the protease-activated receptor 2 (PAR2). Transcriptomic fingerprinting and signaling assays in p11-knockout cells reveal that p11 acts as an amplifier of endogenous PAR2 signaling. PAR2 and p11 are specifically coexpressed in vivo in a subset of sensory neurons, and p11-deficient mice exhibit a blunted PAR2-mediated inflammatory response. Our results establish p11 as a widespread, activity-dependent modulator of GPCR-mediated signaling outcomes across diverse physiological processes.