A covalent allosteric probe for the metabotropic glutamate receptor 2: Design, synthesis and pharmacological characterization.

Covalent labeling of G protein-coupled receptors (GPCRs) by small molecules is a powerful approach to understand binding modes, mechanism of action, pharmacology, and even facilitate structure elucidation. We report the first covalent positive allosteric modulator (PAM) for a class C GPCR, the mGlu(2) receptor. Three putatively covalent mGlu(2) PAMs were designed and synthesized. Pharmacological characterization identified 2 to bind the receptor covalently. Computational modeling combined with receptor mutagenesis revealed T791(7.29x30) as the likely position of covalent interaction. We show how this covalent ligand can be used to characterize the PAM binding mode and that it is a valuable tool compound in studying receptor function and binding kinetics. Our findings advance the understanding of the mGlu(2) PAM interaction and suggest that 2 is a valuable probe for further structural and chemical biology approaches.