Cryo-electron microscopy structures of human thyroid peroxidase (TPO) in complex with TPO antibodies

Abstract

Determination of the structure of the extracellular domain of human thyroid peroxidase (hTPO) by cryo-electron microscopy (cryo-EM) is described. TPO, purified to homogeneity was complexed with the human TPO monoclonal autoantibody 2G4 Fab and also with a mouse monoclonal TPO antibody 4F5 Fab (which competes with autoantibody binding to TPO). Both complexes were analysed by cryo-EM. The two structures (global resolution 3.92Å and 3.4Å for the 2G4 complex and 4F5 complex respectively) show TPO as a monomer with 4 domains; the N-terminal domain, the peroxidase domain (POD), the complement control protein like (CCP) domain and the epidermal growth factor like (EGF) domain which are all visible in the structures. The relative positions of the domains are fixed with a disulphide bond between cysteine residues Cys146 in the POD and Cys756 in the CCP domain preventing significant flexibility of the molecule. The entrance to the enzyme active site, the haem group and the calcium binding site are clearly visible on the opposite side of the TPO molecule from the 2G4 and 4F5 binding sites. Extensive interactions are seen between TPO and the two antibodies which both bind to distinct epitopes on the POD domain, including some residues in the immunodominant region B (IDR-B) mainly via different residues. However the epitopes of the two antibodies contain three shared TPO residues. This is the first high resolution structure of TPO to be reported and it should help guide development of new inhibitors of TPO enzyme activity for therapeutic applications.

Determination of HLA class II risk alleles and prediction of self/non-self-epitopes contributing Hashimoto’s thyroiditis in a group of Iranian patients

“…According to a study by Baker et al [41], speci c residues within the TPO sequence 151-199, including Leu 177, Gly 194, Leu 196, Asn 198, and Gly 199, bind to the Fab region of the anti-TPO antibody's L, H, H, L, and H chains, respectively. Based on these ndings, it can be postulated that the homologous sequence 145-180 of the envelope glycoprotein D in Herpesviruses serves as a critical molecular mimic.…”

The Usefulness of Thyroid Antibodies in the Diagnostic Approach to Autoimmune Thyroid Disease

“…TPOAbs are capable of recognizing discontinuous determinants in TPO, which have been named immunodominant regions A (IDR-A) and B (IDR-B), and several contact residues constituting IDR-A and IDR-B have been identified: 225; 353–363; 377–386; 597–604; 611–618; 620; 624; 627; 630; 646; 707; 713–720; and 766–775 [ 58 , 59 ].…”

The Usefulness of Thyroid Antibodies in the Diagnostic Approach to Autoimmune Thyroid Disease

“…The prevalence of positivity in individuals with AITD is higher than for TgAbs [57]. TPOAbs are capable of recognizing discontinuous determinants in TPO, which have been named immunodominant region A (IDR-A) and B (IDR-B), and several contact residues constituting IDR-A and IDR-B have been identified: 225, 353-363, 377-386, 597-604, 611-618, 620, 624, 627, 630, 646, 707, 713-720, and 766-775 [58,59].…”