Structural studies of thyroid peroxidase show the monomer interacting with autoantibodies in thyroid autoimmune disease

Abstract

25Thyroid peroxidase (TPO) is a critical membrane-bound enzyme involved in the biosynthesis of 26 multiple thyroid hormones, and is a major autoantigen in autoimmune thyroid diseases such as 27 Graves' disease and Hashimoto's thyroiditis. Here we report the biophysical and structural 28 characterisation of two novel TPO constructs containing only the ectodomain of TPO and lacking the 29 propeptide. Both constructs were enzymatically active and able to bind the patient-derived TR1.9 30 autoantibody. Analytical ultra-centrifugation data suggests that TPO can exist as both a monomer 31 and a dimer. Combined with negative stain electron microscopy and molecular dynamics 32 simulations, these data show that TR1.9 autoantibody preferentially binds the TPO monomer, 33 revealing conformational changes that bring together previously disparate residues into a 34 continuous epitope. In addition to providing plausible structural models of a TPO-autoantibody 35 complex, this study provides validated TPO constructs that will facilitate further characterization, 36 and advances our understanding of the structural, functional and antigenic characteristics of TPO, a 37 molecule behind some of the most common autoimmune diseases. 38 39 40 41 48 (Hashimoto's disease) and hyperthyroidism (Grave's disease) 2,3. AITDs are some of the most 49 common autoimmune diseases in the developed world, with Hashimoto's disease being a strong risk 50 factor for thyroid cancer 4. TPO is suspected to be involved in the pathogenesis of Hashimoto's 51 thyroiditis (prevalence 300-2980 cases per 100,000 in the Western world), leading to thyrocyte 52 destruction via CD8+ T-cell infiltration resulting in hypothyroidism 1,3,5. This incidence rate can be 53 compared to other autoimmune diseases -for example type 1 diabetes, which has an incidence in 54 the developed world of 310-570 cases per 100,000 patients -demonstrating the immense disease 55 burden caused by AITDs 5. The pathogeneses that underlies these autoimmune diseases is complex, 56 however the lack of any tertiary or quaternary structure of TPO complicates matters. The absence of 57 a structure in which to understand binding of anti-TPO antibodies, which are prevalent almost 58 ubiquitously (>95%) in cases of destructive thyroiditis, complicates the understanding of the 59 pathogenesis and nature of the disease. The precise mechanism by which these antibodies cause 60 damage is uncertain 2. Additionally, in some cases AITDs can occur without these autoantibodies 61 being present, and transplacental passage of anti-TPO antibodies does not necessarily cause thyroid 62 damage in the offspring 3,6,7. Despite this, transplacental passage of these autoantibodies can 63 potentially have cognitive effects on the child. In addition, antibodies to thyroglobulin (Tg) and 64 thyroid stimulating hormone receptor have been identified in both conditions, indicating that there 65 may be multiple antigens in AITD pathogenesis 2. 66TPO is a member of the animal heme peroxidase family, which also includes myelope...

Presence of IgE Autoantibodies Against Eosinophil Peroxidase and Eosinophil Cationic Protein in Severe Chronic Spontaneous Urticaria and Atopic Dermatitis

“…IgG response to EPX was detected in asthma, 23 and this protein share common epitopes with TPO as they belong to the same family. 24 25 26 …”