Cryo-EM structures of the ß3 adrenergic receptor bound to solabegron and isoproterenol.

The ß3-adrenergic receptor (ß3AR) is the most essential drug target for overactive bladder and has therapeutic potentials for the treatments of type 2 diabetes and obesity. Here, we report the cryo-electron microscopy structures of the ß3AR-Gs signaling complexes with the selective agonist, solabegron and the nonselective agonist, isoproterenol. Comparison of the isoproterenol-, mirabegron-, and solabegron-bound ß3AR structures revealed that the extracellular loop 2 changes its conformation depending on the bound agonist and plays an essential role in solabegron binding. Moreover, ß3AR has an intrinsically narrow exosite, regardless of the agonist type. This structural feature clearly explains why ß3AR prefers mirabegron and solabegron, as the narrow exosite is suitable for binding with agonists with elongated shapes. Our study deepens the understanding of the binding characteristics of ß3AR agonists and may pave the way for developing ß3AR-selective drugs.

Cryo-EM structures of calcium homeostasis modulator channels in diverse oligomeric assemblies.

Calcium homeostasis modulator (CALHM) family proteins are Ca2+-regulated adenosine triphosphate (ATP)-release channels involved in neural functions including neurotransmission in gustation. Here, we present the cryo-electron microscopy (EM) structures of killifish CALHM1, human CALHM2, and Caenorhabditis elegans CLHM-1 at resolutions of 2.66, 3.4, and 3.6 Å, respectively. The CALHM1 octamer structure reveals that the N-terminal helix forms the constriction site at the channel pore in the open state and modulates the ATP conductance. The CALHM2 undecamer and CLHM-1 nonamer structures show the different oligomeric stoichiometries among CALHM homologs. We further report the cryo-EM structures of the chimeric construct, revealing that the intersubunit interactions at the transmembrane domain (TMD) and the TMD-intracellular domain linker define the oligomeric stoichiometry. These findings advance our understanding of the ATP conduction and oligomerization mechanisms of CALHM channels.