Darcis, J. | Search bioRxiv

bioRxiv2026

Atypical GPCR Activation Resolved by Nanobody Engineering

Abstract/ Summary ParagraphG protein-coupled receptors (GPCRs) are the largest family of clinically targeted proteins, yet most therapeutics target a narrow subset of structurally well-behaved receptors. The atypical chemokine receptor ACKR3 defies canonical models, displaying broad ligand recognition, high basal activity, and resistance to inhibition. Using engineered nanobodies, cryo-EM, NMR, and structure-guided pharmacology, we uncover an unconventional activation mechanism in ACKR3 that challenges established paradigms of GPCR activation. We find that receptor activity is controlled by changes in extracellular pocket volume rather than conformational rearrangements in conserved microswitches, and an expanded aromatic cluster at the intracellular transducer binding pocket stabilizes the active state. These findings redefine how GPCRs can be modulated and open new strategies for targeting pharmacologically intractable receptors.

biochemistry↗

bioRxiv2024

ACKR5/GPR182 is a scavenger receptor for the atypical chemokine CXCL17, GPR15L and various endogenous peptides

GPR182/ACKR5, the most recently deorphanized chemokine receptor, is mainly expressed on endothelial cells and was proposed to act as a scavenger regulating the availability of a large set of chemokines. In this study, we first established the exact profiles and ranking of the chemokines binding to the human and mouse GPR182. We confirmed the high promiscuity of GPR182 towards XC, CC and CXC chemokines and a clear difference in the chemokine repertoires of the human and mouse orthologues. We next demonstrated that, beyond classical chemokines, GPR182 exhibits potent binding to the chemoattractant protein GPR15L/C10orf99, the atypical chemokine CXCL17 and various endogenous peptides, mainly from the opioid, apelin, and PACAP families. We also showed that these newly identified ligands engage GPR182 through varied binding modes. While GPR15L, just like classical chemokines, predominantly engages GPR182 via its N terminus, conversely to the C terminus-dependent binding to its cognate receptor GPR15, CXCL17 exhibits a more complex interaction, relying on both the N and C terminus. The binding mode of the newly identified peptide ligands also differ from the interactions with their cognate receptors. Our findings establish the first scavenger receptor for CXCL17 and GPR15L and advance the understanding of GPR182 ligand interactions, suggesting a regulatory role beyond chemokines.

pharmacology and toxicology↗