Pharmacological Characterization of Dopamine Receptor DRD1 Variants and Exploration of Their Allosteric Activation.

G protein-coupled receptors (GPCRs) are major drug targets, yet genetic variations in these receptors can alter drug responses, leading to significant challenges in healthcare. Despite the prevalence of GPCR-targeting drugs, the effects of these genetic variations on receptor function remain underexplored. This study establishes a framework for allosterically rescuing loss-of-function (LoF) variants in GPCRs, using the dopamine receptor D1 (DRD1) as a model. We characterized 49 DRD1 variants from genetic databases and literature, finding that most variants exhibit reduced membrane expression. Structural analysis indicated that variants within the ligand-binding pocket or near critical activation motifs may impair ligand binding or hinder conformational changes during receptor activation, potentially disrupting orthosteric ligand induced signaling. We categorized the variants into three functional groups: those with enhanced G protein signaling, enhanced β-arrestin recruitment, or complete LoF. Among these, 16 variants disrupt G protein signaling, and 27 impair β-arrestin recruitment in HEK293 cells. Notably, defective G protein signaling caused by LoF variants such as T37^1.46K and L66^2.46F were effectively restored using allosteric modulators. These findings highlight the functional impact of DRD1 variants and demonstrate the therapeutic potential of relative selectivity of two signal pathways. This study advances precision medicine by offering strategies to restore receptor function and develop targeted therapies for GPCR-related disorders.