A calcium-sensing receptor mutation causing hypocalcemia disrupts a transmembrane salt bridge to activate beta-arrestin-biased signaling

Gorvin, Caroline M, Babinsky, Valerie N, Malinauskas, Tomas, Nissen, Peter H, Schou, Anders J, Hanyaloglu, Aylin C, Siebold, Christian, Jones, E Yvonne, Hannan, Fadil M ORCID: 0000-0002-2975-5170 and Thakker, Rajesh V (2018) A calcium-sensing receptor mutation causing hypocalcemia disrupts a transmembrane salt bridge to activate beta-arrestin-biased signaling. SCIENCE SIGNALING, 11 (518). eaan3714-.

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Abstract

The calcium-sensing receptor (CaSR) is a G protein–coupled receptor (GPCR) that signals through Gq/11 and Gi/o to stimulate cytosolic calcium (Ca2+i) and mitogen-activated protein kinase (MAPK) signaling to control extracellular calcium homeostasis. Studies of loss- and gain-of-function CASR mutations, which cause familial hypocalciuric hypercalcemia type 1 (FHH1) and autosomal dominant hypocalcemia type 1 (ADH1), respectively, have revealed that the CaSR signals in a biased manner. Thus, some mutations associated with FHH1 lead to signaling predominantly through the MAPK pathway, whereas mutations associated with ADH1 preferentially enhance Ca2+i responses. We report a previously unidentified ADH1-associated R680G CaSR mutation, which led to the identification of a CaSR structural motif that mediates biased signaling. Expressing CaSRR680G in HEK 293 cells showed that this mutation increased MAPK signaling without altering Ca2+i responses. Moreover, this gain of function in MAPK activity occurred independently of Gq/11 and Gi/o and was mediated instead by a noncanonical pathway involving β-arrestin proteins. Homology modeling and mutagenesis studies showed that the R680G CaSR mutation selectively enhanced β-arrestin signaling by disrupting a salt bridge formed between Arg680 and Glu767, which are located in CaSR transmembrane domain 3 and extracellular loop 2, respectively. Thus, our results demonstrate CaSR signaling through β-arrestin and the importance of the Arg680-Glu767 salt bridge in mediating signaling bias.

Item Type:	Article
Uncontrolled Keywords:	Cell Membrane, Humans, Hypocalcemia, Hypoparathyroidism, Calcium, Salts, Receptors, Calcium-Sensing, Pedigree, MAP Kinase Signaling System, Amino Acid Sequence, Base Sequence, Protein Conformation, Sequence Homology, Amino Acid, Mutation, Models, Molecular, Family Health, Female, Male, Hypercalciuria, beta-Arrestins
Depositing User:	Symplectic Admin
Date Deposited:	23 Feb 2018 12:23
Last Modified:	19 Jan 2023 06:39
DOI:	10.1126/scisignal.aan3714
Related URLs:	Author Publisher
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3018360