An Analysis of the Structure and Antigenicity of Different Forms of Human Thyroid Peroxidase

Abstract

Thyroid peroxidase (TPO) is an important enzyme in the production of thyroid hormone and one of the major autoantigens in autoimmune thyroid disease. The gene for human thyroid peroxidase encodes a single 933 amino acid polypeptide chain. However, several reports have suggested that it exists in both high- and low-molecular-weight forms and the exact structure of the native enzyme is not known. We examined the structure of TPO using two monoclonal antibodies against different portions of TPO, a polyclonal mouse antiserum raised against a 300 amino acid fragment of TPO and autoantibodies directed against TPO obtained from patients with autoimmune thyroid disease. Western blots performed under nonreducing conditions identified three bands of approximately 220-230 kDa and two bands of 105 and 110 kDa that appeared to be immunologic TPO. After reduction, the TPO activity migrated as a smear of bands from 105 to 110 kDa, suggesting that the higher molecular weight form of the enzyme is a disulfide-linked dimer. Patients with autoimmune thyroid disease showed higher rates of recognition of the dimer than the reduced monomer when serologic reactivity was analyzed by Western blots. Eighty-three percent (40 of 48) of patients with Graves' disease and 76% (34 of 45) of Hashimoto's disease patients recognized the dimer form of TPO, while 48% (23 of 48) of Graves' and 60% (27 of 45) of Hashimoto's patients recognized reduced monomer TPO, even though both forms were denatured with SDS. Antibodies against different portions of the TPO chain all bound to the 105 kDa bands, indicating that the TPO chain is not bisected during posttranslational processing.(ABSTRACT TRUNCATED AT 250 WORDS)

Genetic analysis of thyroid peroxidase (<i>TPO</i>) gene in patients whose hypothyroidism was found in adulthood in West Bengal, India

“…The human TPO gene (GenBank Accesion # NT_033000) is located on chromosome 2p25 and spans approximately 150 Kb, containing 17 exons [14]. TPO is a membrane-bound glycoprotein (102 kDa), found as a dimer [15]. TPO mutations are typically inherited as autosomal recessive traits [16].…”

Search for the Autoantibody Immunodominant Region on Thyroid Peroxidase: Epitopic Footprinting with a Human Monoclonal Autoantibody Locates a Facet on the Native Antigen Containing a Highly Conformational Epitope

“…Other than the use of chimeric TPO-MPO molecules (which failed to identify the immunodominant region) (35,37), most previous attempts to identify TPO autoantibody epitopes have examined polyclonal autoantibody interactions with polypeptide fragments (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25) with the inherent problem of the highly conformational nature of TPO autoantibody epitopes. However, based on the putative three-dimensional model of TPO, an r-pep fragment (TPO aa residues 742-848) (23), although not defining a precise epitope, may lie in the vicinity of K713 located in the present study.…”

“…It is, therefore, not surprising that identification of conformational, possibly discontinuous, TPO autoantibody epitopes (9 -11) on the native Ag has not been possible using synthetic peptides. Some polypeptide fragments of TPO are recognized by TPO autoantibodies in patients' sera (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25). However, the wide spectrum and large size of these fragments as well as the fact that (in the native structure) polypeptides can traverse the molecule and contribute to widely separated facets on the surface of the protein have not led to deduction of the site of the immunodominant region.…”

Anticorpos anti-tiróide: aspectos metodológicos e importância diagnóstica

“…Hoje sabe-se, com base em estudos comparativos e bioquímicos, que na realidade o "antígeno microssomal" é a peroxidase tiroideana (37)(38)(39)(40). A peroxidase tiroideana (TPO) é uma glicoproteína de membrana composta de 933 aminoácidos e com peso molecular entre 105 e 110kDa na sua forma monomérica, e de 220 a 230kDa na forma dimérica funcional (41). A TPO é uma molécula complexa e vários epítopos foram descritos em sua estrutura, sendo alguns caracterizados como dominantes (42).…”