New Pathogenic Thyrotropin Receptor Mutations Decipher Differentiated Activity Switching at a Conserved Helix 6 Motif of Family A GPCR

Abstract

Context:In this paper we report two new TSH receptor (TSHR) mutations. One mutation (Pro639 6.50 Leu) was identified in two siblings with congenital hypothyroidism, and a second mutation (Cys636 6.47 Arg) was found in a patient suffering from nonautoimmune hyperthyroidism.Both mutations are located in transmembrane helix (TMH) 6 at the conserved Cys 6.47 -Trp(Met) 6.48 -Leu(Ala) 6.49 -Pro 6.50 motif of family A G protein-coupled receptors (GPCR).Objective: To study the pathogenic mechanisms, we tested patients' mutations and further side chain variations regarding their effects on TSHR signaling.Results: Substitution Pro639Leu fully inactivates the promiscuous TSHR for cAMP (Gs) and IP (Gq) signaling. In contrast, Cys636Arg leads to constitutive activation of Gs. Organization of TSHR in oligomers was not modified by mutations at position 636. Interestingly, it is known from crystal structures of GPCR that Pro 6.50 is located at a TMH6 kink-distortion, which is a pivot during activation-related helical movements. However, the cell surface expressions of all mutants at position 639 were comparable to wild type, indicating a helical conformation like wild type. Conclusion:Until now, only naturally occurring constitutively activating mutations in TSHR TMH6 have been reported, but here we present the first pathogenic inactivating mutation (Pro639Leu

Proton transfer during class-A GPCR activation: do the CWxP motif and the membrane potential act in concert?

“…In accordance with the new hypothesis on the functional role of C6.47, mutational variants C6.47T in b 2 AR (Shi et al 2002) and C6.47S/R in thyrotropin hormone receptor (Biebermann et al 2012) result in constitutive G as activation. These mutations are equivalent to protonation of Cys or carrying an extra positive change, thus stabilizing the active state in the presence of DW according to our hypothesis.…”

G-Protein Coupled Receptor 83 (GPR83) Signaling Determined by Constitutive and Zinc(II)-Induced Activity

“…In the thyroid stimulating hormone receptor (TSHR) pathogenic mutants at Cys636 (e.g. Cys636Trp) in TMH6 were characterized as constitutive activating mutations (CAMs) [14], [15]. This position is localized in the highly conserved Cys 6.47 -Trp 6.48 -Leu/Ala 6.49 -Pro 6.50 motif of family A GPCR [16] (the numbers are according to the unified system suggested for family A GPCRs by Ballesteros & Weinstein [17]).…”

A Japanese family with nonautoimmune hyperthyroidism caused by a novel heterozygous thyrotropin receptor gene mutation

“…To date, ~30 constitutively activating TSHR mutations have been reported in nonautoimmune hyperthyroidism (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(15)(16)(17)(18)(19). Most of the activating mutations are present in TMD 1, 2, 3, and 5.…”

“…Activating germline mutations of TSHR cause nonautoimmune sporadic congenital hyperthyroidism or familial nonautoimmune hyperthyroidism (4)(5)(6)(7)(8)(9)(10)(11)(12)(13). To date, gain-of-function mutations in TMD 1, 2, 3, 5, 6, and 7 and in the ECD have been reported (4)(5)(6)(7)(8)(9)(10)(11)(12)(13).…”