Residues 34–39 in the Thyrotropin Receptor are not the Target of Autoantibodies from Sera of Patients with Graves' Disease

Abstract

The thyrotropin receptor (TSHR) and alphal-antytripsin contain a fragment of sequence composed of 6 amino acids in which 5 residues are identical. Previously, we have suggested that this region of similarity [residues 34-39: (EEDFRV) in TSHR] is not the target for Graves' disease patients' autoantibodies. To verify this suggestion, we studied the reaction of patients' sera with alphal-antitrypsin. Two methods were used: TRAK assay, normally designed to estimate anti-TSHR autoantibodies in patients' sera, and immunoblotting. A modified version of the former assay was also used to study the influence of the synthetic peptide, corresponding to the region of similarity in TSHR, on Graves' patients sera or on thyrotropin (TSH) binding, and to study the influence of this peptide antiserum on TSH binding to the receptor. The TSHR stimulating and blocking activity of antisera to this peptide was studied in transfected Chinese hamster ovary cells. No influence of alphal-antitrypsin on the binding of patients' antibodies to the receptor were noticed nor were there reactions of autoantibodies with alphal-antitrypsin. We found that patients with anti-TSHR autoantibodies had a normal concentration of alphal-antitrypsin. A peptide corresponding to residues 34-39 did not influence Graves' patients sera and TSH binding and antiserum to this peptide did not influence TSH binding and adenylate cyclase activity. In summary, the results indicated that the sequence EEDFRV is not the target for patients autoantibodies.

Analysis of Epitopes on the Unrelated Proteins Thyrotropin Receptor and α1‐Antitrypsin which are Recognized by A10 Monoclonal Antibody

“…Alignment of the TSHR amino acid sequence with that of antitrypsin identified five identical amino acids in a short stretch of residues 34–39 (EEDFRV) in TSHR and residues 205–210 (EEDFHV) in antitrypsin. This region is not the target of autoantibodies in the sera of Graves' patients [9].…”