Toshiaki Ban

Role of cysteine residues in the extracellular domain and exoplasmic loops of the transmembrane domain of the TSH receptor: Effect of mutation to serine on TSH receptor activity and response to thyroid stimulating autoantibodies

The extracellular domain of the thyrotropin (TSH) receptor is the primary site with which TSH and receptor autoantibodies interact. Cysteines 494 or 569 in the 1st and 2nd exoplasmic loops, respectively, of the transmembrane domain of the TSH receptor are important in this process or in coupling ligand binding to signal generation. Thus, when either is mutated to serine, a receptor results which has no detectable TSH binding and no cAMP response to TSH or thyroid stimulating autoantibodies after transfection, despite the fact the mutant receptor is normally synthesized, processed, and integrated in the membrane, as evidenced by Western blotting using a TSH receptor-specific antibody. Additional site directed mutagenesis studies are performed in order to identify cysteine residues in the extracellular domain of the receptor which, with cysteines 494 and 569, are important for tertiary structure and receptor bioactivity.

Structure and Regulated Expression of the TSH Receptor Gene: Differences and Similarities to Gonadotropin Receptors

Glycoprotein hormones—lutropin/chorionic gonadotropin (LH/CG), follicle stimulating hormone (FSH), and thyrotropin (TSH)—have a high degree of primary and tertiary structure similarity, yet are target tissue specific (1–5). The structural similarities of the hormones are complemented by functional similarities (1–5). Thus, all are well recognized to activate the cAMP signal transducing system, and all modulate both growth and differentiation of their respective target tissues. It is increasingly evident, in addition, that all depend on the action of other hormones, such as insulin and insulin-like growth factor I (IGF-I), to regulate growth and differentiated function (6–8).