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The calcium-sensing receptor (CaSR), a cell-surface sensor for Ca.sup.2+, is the master regulator of calcium homeostasis in humans and is the target of calcimimetic drugs for the treatment of parathyroid disorders.sup.1. CaSR is a family C G-protein-coupled receptor.sup.2 that functions as an obligate homodimer, with each protomer composed of a Ca.sup.2+-binding extracellular domain and a seven-transmembrane-helix domain (7TM) that activates heterotrimeric G proteins. Here we present cryo-electron microscopy structures of near-full-length human CaSR in inactive or active states bound to Ca.sup.2+ and various calcilytic or calcimimetic drug molecules. We show that, upon activation, the CaSR homodimer adopts an asymmetric 7TM configuration that primes one protomer for G-protein coupling. This asymmetry is stabilized by 7TM-targeting calcimimetic drugs adopting distinctly different poses in the two protomers, whereas the binding of a calcilytic drug locks CaSR 7TMs in an inactive symmetric configuration. These results provide a detailed structural framework for CaSR activation and the rational design of therapeutics targeting this receptor. Cryo-EM structures of human calcium-sensing receptor reveal intrinsic asymmetry in the receptor homodimer upon activation that is stabilized by calcimimetic drugs adopting distinct poses in the two protomers, priming one protomer for G-protein coupling., Author(s): Yang Gao [sup.1] [sup.2] , Michael J. Robertson [sup.1] [sup.2] , Sabrina N. Rahman [sup.4] , Alpay B. Seven [sup.1] [sup.2] , Chensong Zhang [sup.1] [sup.2] , Justin G. [...]

Family C G-protein-coupled receptors (GPCRs) operate as obligate dimers with extracellular domains that recognize small ligands, leading to G-protein activation on the transmembrane (TM) domains of these receptors by an unknown mechanism.sup.1. Here we show structures of homodimers of the family C metabotropic glutamate receptor 2 (mGlu2) in distinct functional states and in complex with heterotrimeric G.sub.i. Upon activation of the extracellular domain, the two transmembrane domains undergo extensive rearrangement in relative orientation to establish an asymmetric TM6-TM6 interface that promotes conformational changes in the cytoplasmic domain of one protomer. Nucleotide-bound G.sub.i can be observed pre-coupled to inactive mGlu2, but its transition to the nucleotide-free form seems to depend on establishing the active-state TM6-TM6 interface. In contrast to family A and B GPCRs, G-protein coupling does not involve the cytoplasmic opening of TM6 but is facilitated through the coordination of intracellular loops 2 and 3, as well as a critical contribution from the C terminus of the receptor. The findings highlight the synergy of global and local conformational transitions to facilitate a new mode of G-protein activation. Cryo-electron microscopy structures show that metabotropic glutamate receptor 2 forms a dimer to which only one G protein is coupled, revealing the basis for asymmetric signal transduction., Author(s): Alpay B. Seven [sup.1] , Ximena Barros-Álvarez [sup.1] , Marine de Lapeyrière [sup.2] , Makaía M. Papasergi-Scott [sup.1] , Michael J. Robertson [sup.1] , Chensong Zhang [sup.1] , Robert [...]