Loss-of-function GalphaS rare disease variants exert mutation-specific effects on GPCR signaling

G protein–coupled receptors (GPCRs) are transmembrane detectors of extracellular signals that activate heterotrimeric G proteins to regulate intracellular responses. Because there are only 16 Galpha proteins that can couple to GPCRs, variation in a single Galpha can affect the function of numerous receptors. Here, we investigated two mutant forms of GalphaS (L388R and E392K) that are associated with pseudohypoparathyroidism type Ic (PHPIc), a maternally inherited rare disease. GalphaS is encoded by an imprinted gene, resulting in the mutant form of GaalphaS being the only version of the protein present in certain tissues, which leads to tissue- specific disease manifestations. By integrating data from 3D structures, GPCR-G protein coupling specificity, transcriptomics, biophysics, and molecular dynamics with systems pharmacology modeling, we identified GPCRs whose signaling could be altered by GalphaS mutations in the kidney, a tissue involved in the pathophysiology of PHPIc. Analysis of G protein activation by the parathyroid hormone receptor 1 (PTH1R) revealed that L388R impaired GalphaS interaction with the receptor, whereas E392K reduced the receptor-induced activation of heterotrimeric Gs. This indicates that different signal transduction steps can be altered by specific GalphaS mutants associated with the same disease. These findings highlight the importance of investigating mutation-specific perturbations in GPCR signaling to suggest patient-specific treatment strategies. Furthermore, our methods provide a blueprint for interrogating GPCR signaling diversity in different physiological and pathophysiological contexts.