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Rearrangement of the Extracellular Domain/Extracellular Loop 1 Interface Is Critical for Thyrotropin Receptor Activation.
Schaarschmidt J, Nagel MB, Huth S, Jaeschke H, Moretti R, Hintze V, von Bergen M, Kalkhof S, Meiler J, Paschke R
(2016) J Biol Chem 291: 14095-108
MeSH Terms: Animals, CHO Cells, Cricetinae, Cricetulus, Glycosylation, Humans, Mass Spectrometry, Models, Molecular, Mutation, Proteolysis, Receptors, Thyrotropin, Surface Plasmon Resonance
Show Abstract · Added April 8, 2017
The thyroid stimulating hormone receptor (TSHR) is a G protein-coupled receptor (GPCR) with a characteristic large extracellular domain (ECD). TSHR activation is initiated by binding of the hormone ligand TSH to the ECD. How the extracellular binding event triggers the conformational changes in the transmembrane domain (TMD) necessary for intracellular G protein activation is poorly understood. To gain insight in this process, the knowledge on the relative positioning of ECD and TMD and the conformation of the linker region at the interface of ECD and TMD are of particular importance. To generate a structural model for the TSHR we applied an integrated structural biology approach combining computational techniques with experimental data. Chemical cross-linking followed by mass spectrometry yielded 17 unique distance restraints within the ECD of the TSHR, its ligand TSH, and the hormone-receptor complex. These structural restraints generally confirm the expected binding mode of TSH to the ECD as well as the general fold of the domains and were used to guide homology modeling of the ECD. Functional characterization of TSHR mutants confirms the previously suggested close proximity of Ser-281 and Ile-486 within the TSHR. Rigidifying this contact permanently with a disulfide bridge disrupts ligand-induced receptor activation and indicates that rearrangement of the ECD/extracellular loop 1 (ECL1) interface is a critical step in receptor activation. The experimentally verified contact of Ser-281 (ECD) and Ile-486 (TMD) was subsequently utilized in docking homology models of the ECD and the TMD to create a full-length model of a glycoprotein hormone receptor.
© 2016 by The American Society for Biochemistry and Molecular Biology, Inc.
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12 MeSH Terms
A newly discovered TSHR variant (L665F) associated with nonautoimmune hyperthyroidism in an Austrian family induces constitutive TSHR activation by steric repulsion between TM1 and TM7.
Jaeschke H, Schaarschmidt J, Eszlinger M, Huth S, Puttinger R, Rittinger O, Meiler J, Paschke R
(2014) J Clin Endocrinol Metab 99: E2051-9
MeSH Terms: Adult, Austria, Base Sequence, Family Health, Female, Goiter, Nodular, Humans, Hyperthyroidism, Pedigree, Point Mutation, Pregnancy, Pregnancy Complications, Receptors, Thyrotropin, Stereoisomerism
Show Abstract · Added January 24, 2015
OBJECTIVE - New in vivo mutations in G protein-coupled receptors open opportunities for insights into the mechanism of receptor activation. Here we describe the molecular mechanism of constitutive TSH receptor (TSHR) activation in an Austrian family with three generations of familial nonautoimmune hyperthyroidism.
PATIENTS - The index patient was diagnosed with hyperthyroidism during her first pregnancy. Her first two children were diagnosed with hyperthyroidism at the age of 11 and 10 years, respectively. TSH suppression was also observed in the third child at the age of 8 years, who has normal free T4 levels until now. TSH suppression in infancy was observed in the fourth child. The mother of the index patient was diagnosed with toxic multinodular goiter at the age of 36 years.
METHODS - DNA was extracted from blood samples from the index patient, her mother, and her four children. Screening for TSHR mutations was performed by high-resolution melting assays and subsequent sequencing. Elucidation of the underlying mechanism of TSHR activation was carried out by generation and structural analysis of TSHR transmembrane homology models and verification of model predictions by functional characterization of receptor mutations.
RESULTS AND CONCLUSIONS - A newly discovered TSHR mutation L665F in transmembrane helix 7 of the receptor was detected in six members of this family. Functional characterization of L665F revealed constitutive activation for the Gs pathway and thus represents the molecular cause for hyperthyroidism in this family. The constitutive activation is possibly linked to a steric clash introduced by the L665F mutation between transmembrane helices 1 and 7.
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14 MeSH Terms