Structural insight into the activation of adenosine A2AR/A2BR by the dual-agonist MRS3997

Abstract

Abstract A 1 R, A 2A R, A 2B R, and A 3 R adenosine receptors comprise a G protein-coupled receptor (GPCR) subfamily that regulates many bodily processes. Subtype-selective agonists potentially treat inflammatory and ischemic conditions. The dual A 2A R/A 2B R agonist MRS3997 protects post-ischemic brain during prolonged inflammation. However, despite known A 2A R and A 2B R structural and pharmacological differences, MRS3997’s activation mechanisms at A 2A R/A 2B R remain unclear. Our cryo-electron microscopy (cryo-EM) structures of both MRS3997-bound A 2A R and A 2B R show adenine with a conserved orthosteric binding mode, while the 6-bromoindole moiety adopts distinct orientations. In A 2A R, the bromoindole group adopts a vertical conformation adjacent to the extracellular vestibular ECL2-ECL3 salt bridge. However, in A 2B R, it extends laterally into a secondary pocket. Mutagenesis supports models involving distinct binding orientations, and molecular dynamics simulations suggest the bromoindole samples both vertical and horizontal orientations within the A 2B R subpocket. These structural and pharmacological results, along with structure-activity relationship data, will guide adenosine receptor agonist rational design, improving potency/selectivity.