Development of antibody stabilizing active or inactive state of GPCRs.

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G-protein-coupled receptors 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 G-protein-coupled receptors result in a cellular response through the activation of G proteins. The adenosine A2a receptor(A2AR) is responsible for regulating blood flow to the cardiac muscle and is important in the regulation of glutamate and dopamine release in the brain. Here we report the raising of a mouse monoclonal antibody against human A2AR that prevents agonist but not antagonist binding to the extracellular ligand-binding pocket, and describe the structure of A2AR in complex with the antibody Fab fragment(Fab2838). This structure reveals that Fab2838 recognizes the intracellular surface of A2AR and that its complementarity-determining region, CDR-H3, penetrates into the receptor. CDR-H3 is located in a similar position to the G-protein carboxy-terminal fragment in the active opsin structure and to CDR-3 of the nanobody in the activeβ2-adrenergic receptor structure, but locks A2AR in an inactive conformation.