Structural Studies of Thyroid Peroxidase Show the Monomer Interacting With Autoantibodies in Thyroid Autoimmune Disease

Abstract

Thyroid peroxidase (TPO) is a critical membrane-bound enzyme involved in the biosynthesis of multiple thyroid hormones, and is a major autoantigen in autoimmune thyroid diseases such as destructive (Hashimoto) thyroiditis. Here we report the biophysical and structural characterization of a novel TPO construct containing only the ectodomain of TPO and lacking the propeptide. The construct was enzymatically active and able to bind the patient-derived TR1.9 autoantibody. Analytical ultracentrifugation data suggest that TPO can exist as both a monomer and a dimer. Combined with negative stain electron microscopy and molecular dynamics simulations, these data show that the TR1.9 autoantibody preferentially binds the TPO monomer, revealing conformational changes that bring together previously disparate residues into a continuous epitope. In addition to providing plausible structural models of a TPO-autoantibody complex, this study provides validated TPO constructs that will facilitate further characterization, and advances our understanding of the structural, functional, and antigenic characteristics of TPO, an autoantigen implicated in some of the most common autoimmune diseases.

Deleterious Mutations in the TPO Gene Associated with Familial Thyroid Follicular Cell Carcinoma in Dutch German Longhaired Pointers

“…The EGF-like domain is involved in ligand recognition and protein–protein interaction. The amino acid changes in the region may change the three-dimensional structure, which could impact the catalytic activity or the autoimmunity of TPO [ 48 ].…”

“…The EGF-like domain is involved in ligand recognition and protein-protein interaction. The amino acid changes in the region may change the three-dimensional structure, which could impact the catalytic activity or the autoimmunity of TPO [48]. Except for the 2 deleterious mutations, 4 synonymous mutations and 31 intronic variants were also identified in the TPO gene of affected dogs.…”

Cellular and molecular basis of thyroid autoimmunity

“…Additionally, the antigenantibody interaction is connected with conformational changes in TPO that bring together previously far apart residues into a continuous epitope. This may explain the previously contradictory epitope mapping data reported by various research teams that IDR-A and IDR-B include residues theoretically too far apart to be involved by single autoantibody complementarity-determining regions based on previous modeling (14,20).…”

“…Specific patterns of TPOAb recognition are stable in an individual over time and genetically inherited in families ( 16 , 19 ). Recently reported data shed new light on the interaction between TPO and autoantibodies ( 14 , 20 ). Unexpectedly, it seems that monomeric TPO is preferentially recognized by autoantibodies, whereas in dimeric mature, TPO the binding sites are hidden.…”

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

“…To date, the structure of TPO has not been solved despite numerous attempts ( Gardas et al 1997 , Hendry et al 1999 , Hendry 2001 a , Thomas 2019 , Williams et al 2020 ), and in order to study the relationship between TPO structure and function, several models of TPO have been produced ( Hendry 2001 a , Hobby et al 2000 , Le et al 2015 , Williams et al 2018 , 2020 ).…”