G protein-coupled receptor inactivation by an allosteric inverse-agonist antibody

摘要

G protein-coupled receptors (GPCRs) are the largest class of cell-surface receptors, and these membrane proteins exist in equilibrium between inactive and active states.^- Conformational changes induced by extracellular ligands binding to GPCRs result in a cellular response through the activation of G-proteins. The A2A adenosine receptor (A2AAR) is responsible for regulating blood flow to the cardiac muscle and is important in the regulation of glutamate and dopamine release in the brain. In this study, we have successfully raised a mouse monoclonal antibody against human A2AAR that prevents agonist but not antagonist binding to the extracellular ligand-binding pocket. The structure of the A2AAR-antibody Fab fragment (Fab2838) complex reveals that the fragment, unexpectedly, recognises the intracellular surface of A2AAR and that its complementarity determining region, CDR-H3, penetrates into the receptor. CDR-H3 is located in a similar position to the G-protein C-terminal fragment in the active opsin structure and to the CDR-3 of the nanobody in the active β2 adrenergic receptor structure but locks the A2AAR in an inactive conformation. These results shed light on a novel strategy to modulate GPCR activity.