TARGETING THE ORPHAN GPCR GPR88 USING NANOBODIES (VHH)

GPR88 is an orphan G protein-coupled receptor (GPCR) highly enriched in striatal medium spiny neurons, crucial for motor control, motivation, and emotional behaviors. In mice, Gpr88 deletion alters anxiety, motor stereotypies, and disrupts striatal signaling, underscoring its importance in basal ganglia function. Human genome-wide association studies link GPR88 polymorphisms to neuropsychiatric disorders like bipolar disorder, schizophrenia, and Parkinson’s disease. Despite its genetic and functional significance, GPR88 pharmacology has been poorly understood.
Recent structural studies have advanced GPR88 biology. Cryo-EM structures revealed GPR88 has an atypical GPCR architecture with a deeply occluded orthosteric pocket and strong constitutive coupling to Gi, explaining the scarcity of small-molecule ligands and challenges in classical pharmacological modulation. Few synthetic agonists, such as 2-PCCA and compound 19, exist, all with limited potency.
To address these challenges, we explored nanobodies (VHHs) as an alternative. Nanobodies, single-domain antibody fragments from camelid immunoglobulins, offer high affinity, specificity, reduced size, and favorable biophysical properties. They stabilize GPCR conformations and modulate receptor activity through cryptic binding sites. We identified and characterized GPR88-targeting nanobodies that selectively recognize receptor conformations and modulate Gi signaling. These nanobodies are novel tools to study GPR88 signaling mechanisms and offer new therapeutic opportunities for targeting this orphan GPCR in neuropsychiatric disorders.