TSHR169 Antigen Specifically Binds to the Thyroid-stimulating Autoantibody, Representing an Effective Biomarker for Graves’ Disease

The thyroid-stimulating hormone receptor (TSHR) is one of the thyroid antigens responsible for Graves’ disease and acts as a biomarker for early detection. The purpose of this study was to computationally compare the effectiveness of TSHR56 and TSHR169 fragments in binding to the thyroid-stimulating human monoclonal autoantibody (M22) at the molecular level. The 3D model of M22 was obtained from RCSB (ID 3G04), while the TSHR antigen models were submitted to homology modeling using SWISSMODEL and PhyreV2.0 server to predict the protein structures. The model was validated by generating a Ramachandran plot with the RAMPAGE server. Prediction of the molecular interaction between TSHR and M22 was performed using the HADDOCK web server (version 2.2). Analysis of the binding affinity was conducted using the PRODIGY server. Interactions within the TSHR-M22 complex were analyzed using DIMPLOT. The antigen models had reliability scores of 100% and 97.7% for TSHR56 and TSHR169, respectively. The results of the molecular docking analysis revealed a better HADDOCK score for TSHR169 (-144.7 ± 2.4) compared to TSHR56 (-53.3 ± 10.1). However, the affinity of TSHR56 (-10.1 Kcal/mol) and TSHR169 (-10.2 Kcal/mol) were not significantly different. The results of the TSHR-M22 interaction specificity analysis suggested that TSHR169 is superior to TSHR56, as the number of interacting amino acids was comparable to the control (TSHR260-M22). It can be concluded that TSHR169 represents a specific full-length TSHR antigen and can be developed as biomarker for Graves’ disease.