Pleiotropic pathways of extracellular calcium sensing

Summary The human calcium-sensing receptor (CaSR) detects fluctuations in the circulating Ca2+ concentration and maintains extracellular Ca2+ homeostasis by regulating parathyroid hormone secretion. In addition, the receptor mediates a wide range of cellular processes unrelated to Ca2+ balance such as fetal development. Malfunction of CaSR is associated with a vareity of Ca2+ homeostatic disorders including potentially life threatening neonatal hypercalcaemic conditions. Abnormalities in the CaSR gene has also been implicated in other diseases including cancer and Alzheimer’s disease. The functional diversity of the CaSR results from its ability to signal through all four subtypes of G proteins, including Gq/11, Gi/o, Gs, and G12/13. We have used Cryo-electron microscopy (EM) to solve the structures of active CaSR complexed with different G proteins. In this application, we will build upon this structural data to explore how the CaSR achieves G protein selectivity and promiscuity using structure-based functional studies. We will also assess the signaling effects of naturally occurring mutations in the receptor that are linked to Ca2+ metabolic and other disorders. We will determine the impact of these mutations on cell surface expression as well as activation of each of the four G protein families. In addition, we will explore the ability of positive and negative allosteric modulators to normalize receptor signaling. Finally, we will initiate structural studies to understand the mechanistic basis for naturally occurring mutations that differentially impact the various G protein subtypes. Our work will elucidate the intracellular signaling mechanisms of the CaSR and map out the functional roles of disease mutations. The information gathered from our studies will assist the design of therapeutics targeting specific CaSR mutations and guide precision medicine efforts in the future.