Nour Aldin Kahlous: Molecular Determinants of Ligand Pharmacology in G Protein-Coupled Receptors: Unlocking the Principles of Ligand-Receptor Recognition and Signalling

Abstract

G protein-coupled receptors (GPCRs) are the largest family of membrane proteins and a major class of drug targets. Despite significant advances in GPCR structural and pharmacological research, understanding how ligands achieve selectivity, receptor activation, and biased signalling remains a central challenge. This thesis combines computational and experimental approaches to study GPCR function and to develop strategies for drug discovery. In Paper I, we investigated endogenous ligand selectivity in the β2 adrenergic receptor (β2R) and the D1 dopamine receptor (D1R), which share high structural and sequence similarity. Our results show that selectivity arises from interaction networks within and outside the orthosteric binding site, thereby advancing our understanding of GPCR ligand selectivity. In Papers II and III, we developed a computational framework to predict ligand efficacy by quantifying affinity differences between active and inactive receptor conformations. This approach enabled the rational design of β2R ligands with tailored efficacy profiles. In Paper IV, we investigated signalling bias at β2R and identified structural determinants of G protein-coupled receptor kinase 2 biased signalling, enabling the design of pathway-selective ligands. In Paper V, large-scale structure-based virtual screening resulted in the discovery of classical and unconventional D1R ligands and revealed determinants of receptor activation. Finally, in Papers III, VI, and VII, protein structure prediction methods generated models that supported modelling of receptor-ligand complexes and mechanistic studies of receptor activation. Together, this work provides a general framework for understanding GPCR pharmacology and guiding the design of selective and effective therapeutics.