Basis for antibody- and hormone-mediated activation of TSHR in Graves’ disease

Abstract

Thyroid stimulating hormone (TSH), through activation of its G protein–coupled receptor TSHR, controls the synthesis of thyroid hormone (TH), an essential metabolic hormone. Aberrant signaling of TSHR by autoantibodies causes Graves′ disease and hypothyroidism that affect millions of patients worldwide. Here we report the active structures of TSHR with TSH and an activating autoantibody M22, both bound to an allosteric agonist ML109, as well as an inactive TSHR structure with inhibitory antibody K1–70. Both TSH and M22 push the extracellular domain (ECD) of TSHR into the upright active conformation. In contrast, K1–70 blocks TSH binding and is incapable of pushing the ECD to the upright conformation. Comparisons of the active and inactive structures of TSHR with those of the luteinizing hormone–choriogonadotropin receptor (LHCGR) reveal a universal activation mechanism of glycoprotein hormone receptors, in which a conserved 10-residue fragment (P10) from the hinge C–terminal loop mediated interactions from the receptor ECD to its transmembrane domain. One surprisingly feature is that there are over 15 cholesterols surrounding TSHR, supporting its preferential location in lipid rafts. These structures also highlight a common mechanism for TSH and autoantibody M22 to activate TSHR, thus providing the molecular basis for Graves′ disease.

Universal mechanism of hormone and allosteric agonist mediated activation of glycoprotein hormone receptors as revealed by structures of follicle stimulating hormone receptor

“…2c, d). Interestingly, 13 cholesterol and 5 lipid molecules were found surrounding the FSHR TMD, like a belt, which was similar to what has been observed in TSHR structures (PDB: 7XW5) 16 (Fig. 1a, Extended Data Fig.…”

“…2c, d), which is also observed in the crystal structure of FSH-FSHR_ECD complex 11 . Similar hinge loop-hormone interactions were also observed in the structures of both CG-LHCGR-Gs and TSH-TSHR-Gs complexes 16, 17 . A conserved sulfated tyrosine at the hinge loop (Y335 from FSHR, Y331 from LHCGR and Y385 from TSHR) was shown to involve in hormone binding and activation of the receptor 31, 32 .…”

“…Compared to LHCGR and TSHR, the location of Cpd-21f is almost completely overlapped with the LHCGR ligand org43553 and the TSHR ligand ML-109 (Fig. 5a), indicating a similar activation mechanism of glycoprotein hormone receptors by small molecular allosteric agonists 16,17 . FSHR, LHCGR, and TSHR share similar allosteric binding pockets as their high similarities in their TMD sequences and structures, which hinder the development of selective allosteric agonists targeting these important receptors (Extended Data Fig.…”

“…Unlike most of class A GPCRs, the glycoprotein hormone-binding sites are located at the distal end of the elongated ECDs of glycoprotein hormone receptors [15][16][17] . The common "push and pull" model of glycoprotein hormone-induced receptor activation suggests that glycoprotein hormone receptors have evolved a unique paradigm for activation signal transduced from their ECD to TMD, which is distinct from other class A GPCRs.…”

“…There are three members of glycoprotein hormone receptors, FSHR, LHCGR and TSHR, which are activated to mainly couple the Gs protein and lead to up-regulation of the secondary message cAMP in cells 14 . Most recently, the cryo-electron microscopy (cyro-EM) structures of CG-LHCGR-Gs and TSH-TSHR-Gs complexes have also been determined [15][16][17] , further providing insights into hormone specificity and hormone-induced receptor activation. The structures of CG-LHCGR-Gs and TSH-TSHR-Gs complexes suggested that there might be a conserved activation mechanism among glycoprotein hormone receptors.…”