title: Defining structural and functional dimensions of the extracellular thyrotropin receptor region.
abstract: The extracellular region of the thyrotropin receptor (TSHR) can be subdivided into the leucine-rich repeat domain (LRRD) and the hinge region. Both the LRRD and the hinge region interact with thyrotropin (TSH) or autoantibodies. Structural data for the TSHR LRRD were previously determined by crystallization (amino acids Glu(30)-Thr(257), 10 repeats), but the structure of the hinge region is still undefined. Of note, the amino acid sequence (Trp(258)-Tyr(279)) following the crystallized LRRD comprises a pattern typical for leucine-rich repeats with conserved hydrophobic side chains stabilizing the repeat fold. Moreover, functional data for amino acids between the LRRD and the transmembrane domain were fragmentary. We therefore investigated systematically these TSHR regions by mutagenesis to reveal insights into their functional contribution and potential structural features. We found that mutations of conserved hydrophobic residues between Thr(257) and Tyr(279) cause TSHR misfold, which supports a structural fold of this peptide, probably as an additional leucine-rich repeat. Furthermore, we identified several new mutations of hydrophilic amino acids in the entire hinge region leading to partial TSHR inactivation, indicating that these positions are important for intramolecular signal transduction. In summary, we provide new information regarding the structural features and functionalities of extracellular TSHR regions. Based on these insights and in context with previous results, we suggest an extracellular activation mechanism that supports an intramolecular agonistic unit as a central switch for activating effects at the extracellular region toward the serpentine domain.
authors.affiliation: Department for Structural Biology, Leibniz-Institut für Molekulare Pharmakologie, D-13125 Berlin, Germany.
authors.forename: Gunnar
authors.initials: G
authors.lastname: Kleinau
authors.forename: Sandra
authors.initials: S
authors.lastname: Mueller
authors.forename: Holger
authors.initials: H
authors.lastname: Jaeschke
authors.forename: Paul
authors.initials: P
authors.lastname: Grzesik
authors.forename: Susanne
authors.initials: S
authors.lastname: Neumann
authors.forename: Anne
authors.initials: A
authors.lastname: Diehl
authors.forename: Ralf
authors.initials: R
authors.lastname: Paschke
authors.forename: Gerd
authors.initials: G
authors.lastname: Krause
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D019556:COS Cells; D002417:Cattle; D002522:Chlorocebus aethiops; D017124:Conserved Sequence; D000242:Cyclic AMP / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D007295:Inositol Phosphates / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011989:Receptors, Thyrotropin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D013972:Thyrotropin / Q000378:metabolism
chemical_list: D007295:Inositol Phosphates; D011989:Receptors, Thyrotropin; D013972:Thyrotropin; D000242:Cyclic AMP