title: Cysteine 390 mutation of the TSH receptor modulates its ectodomain as an inverse agonist on the serpentine domain with decrease in basal constitutive activity.
abstract: Mutations of individual cysteine residues at codon 301, 390, 398 and 408 of the thyrotropin receptor (TSHr) to serine resulted in cell surface expression of only C301S and C390S mutants. C390S mutation was a silencing mutation with decreased basal constitutive activity. Although the C301S and C390S mutants did not show any significant TSH binding, they generated cyclic AMP upon TSH stimulation. These mutants were also able to interact with stimulating and blocking anti-TSHr antibodies. In fact, C390S receptor is a more sensitive tool for blocking antibody detection than wild type receptor. Introduction of C390S to activating mutations in the ectodomain (S281N), exloop (I486F) and transmembrane (D633H) segments could not mute/nullify receptor activation. These data indicate that the C390S ectodomain behaves as a more effective inverse agonist on the noisy transmembrane segment and suggest that the basal and activated states of the receptor operate through two independent pathways.
authors.affiliation: SingHealth Research Facilities, Singapore Health Service, 5, Hospital Drive Block A, #03-04, Singapore 169609, Republic of Singapore. gechsc@sgh.com.sg
authors.forename: Su-Chin
authors.initials: SC
authors.lastname: Ho
authors.forename: Sui-Sin
authors.initials: SS
authors.lastname: Goh
authors.forename: Qing
authors.initials: Q
authors.lastname: Su
authors.forename: Daphne Hsu-Chin
authors.initials: DH
authors.lastname: Khoo
mesh_terms: D000818:Animals; D001323:Autoantibodies / Q000032:analysis / Q000502:physiology; D002460:Cell Line; D003062:Codon; D000242:Cyclic AMP / Q000378:metabolism; D003545:Cysteine / Q000032:analysis / Q000235:genetics* / Q000502:physiology; D006388:Hemagglutinins; D006801:Humans; D018828:Immunoglobulins, Thyroid-Stimulating / Q000032:analysis / Q000502:physiology; D009154:Mutation; D017434:Protein Structure, Tertiary; D011962:Receptors, FSH / Q000235:genetics / Q000502:physiology; D011974:Receptors, LH / Q000235:genetics / Q000502:physiology; D011989:Receptors, Thyrotropin / Q000032:analysis / Q000737:chemistry / Q000235:genetics* / Q000276:immunology / Q000502:physiology*; D012694:Serine / Q000032:analysis / Q000235:genetics; D015398:Signal Transduction; D037941:Silencer Elements, Transcriptional / Q000235:genetics
chemical_list: D001323:Autoantibodies; D003062:Codon; D006388:Hemagglutinins; D018828:Immunoglobulins, Thyroid-Stimulating; D011962:Receptors, FSH; D011974:Receptors, LH; D011989:Receptors, Thyrotropin; C094372:thyrotropin-binding inhibitory immunoglobulin; D012694:Serine; D000242:Cyclic AMP; D003545:Cysteine