Rare variant in intracellular loop-2 of the ghrelin receptor reveals novel mechanisms of GPCR biased signaling and trafficking
Research Poster Health & Life Sciences 2025 Graduate ExhibitionPresentation by Elsa Balfe
Exhibition Number 188
Abstract
G protein-coupled receptors (GPCR’s) are the largest family of membrane proteins and comprise more than one-third of all FDA-approved drugs. GPCRs convert extracellular stimuli into physiological responses by coupling to intracellular transducers — namely, G proteins and B-arrestin (Barr). To enhance the safety and efficacy of GPCR-directed therapeutics, leveraging the ‘biased signaling’ of intracellular transducers has shown promise. Previous work with the growth hormone secretagogue receptor (GHSR), a GPCR drug target for metabolic diseases, has revealed two ‘bias hotspots’ within intracellular loop 2 (ICL2) of the receptor, Pro148ICL2 and Leu149ICL2. To determine if these sites exhibit natural variation in humans, we identified an ultra-rare mutation in GHSR-Leu149ICL2, GHSR-Leu149Pro. To characterize the mutation, we employed a variety of biochemical approaches to assess subcellular distribution, receptor trafficking, and biased signaling of the GHSR-Leu149Pro relative to the wild-type GHSR. We found that the GHSR-Leu149Pro mutant confers complete Barr-bias (i.e., no G protein signaling) by disrupting receptor partitioning within lipid-dependent subcellular microdomains. Moreover, our computational analyses suggest that GHSR-Leu149Pro exhibits these unique effects via the destabilization of ICL2 conformations. These results provide a rational basis for ICL2-targeted drug development. Importantly, these findings support that rare, natural GPCR mutations with such dramatic biochemical effects could plausibly manifest clinically-relevant outcomes. In future studies, we will identify and characterize natural mutations in phylogenetically-related GPCRs bearing this ICL2 ‘bias hotspot’ and ascertain their biochemical phenotypes in vitro. These efforts will further illuminate the clinical relevance of the ‘GPCRome’ and potentially, identify novel drug targets.
Importance
G protein-coupled receptors (GPCR’s) are the most common pharmaceutical drug target, but their clinical utility is often limited by side effects due to poor specificity. One potential solution is to design drugs that ‘bias’ GPCRs towards only the therapeutic signaling pathway(s), while simultaneously blocking the pathways responsible for side effects. Our research focuses on a promising GPCR drug target, the growth hormone secretagogue receptor (GHSR), which responds to “hunger hormone” ghrelin. Using cutting-edge tools in GPCR biology, we investigate the molecular mechanisms of ‘biased’ signaling by identifying and characterizing naturally-occurring GHSR mutations. Ultimately, our work aims to demonstrate the therapeutic potential of GPCR biased signaling by combining human genetics with mechanism-driven drug development.