Molecular Basis of PAC1R Allosteric Modulation with Lipids in Membranes

The pituitary adenylate cyclase-activating polypeptide receptor I (PAC1R) represents a highly sought-after therapeutic target for chronic pain, migraine, and post-traumatic stress. As a class B G protein-coupled receptor (GPCR), the PAC1R is highly expressed throughout the neuronal and central nervous system membranes, with the receptor subject to hormone activation and subsequent signal transduction. Despite its desirable indication, small molecule agonists for PAC1R have been notoriously difficult to develop due to competition with PACAP. For this reason, allosteric activation of the receptor has emerged as a promising pathway. To probe potential allosteric sites, herein, we present a study of the receptor in biomimetic concentrations of lipid membranes. Our results reveal that cholesterol recognizes two canonical and two non-canonical binding sites at PAC1R, which may influence critical residues in the transmembrane domain and PAC1R activation. Also, our simulations suggest the glycolipid GM3 interacts with PAC1R in both the extracellular and transmembrane domains. These lipid binding hotspots may hold high potential for advancing our understanding of class B GPCR signaling and the discovery of new molecules targeting PAC1R. Statement of SignificanceThe PAC1R is a highly sought after therapeutic target in the GPCR family. Understanding its natural process signaling is highly interesting in identifying new modes of control and is currently not well established. This work uses coarse-grained molecular dynamics simulations to examine diverse PAC1R models interactions with their endogenous lipid bilayer in compositions that match the regions in the brain where the receptor is expressed. Two lipids, cholesterol and GM3, have been previously identified in similar receptors as allosteric modulators and were specifically examined in this study. This work also showcases multiple new lipid binding sites at transmembrane and extracellular sites highly implicated in PAC1R signaling.