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

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

One of the probable hypotheses for the onset of autoimmunity is molecular mimicry. This study aimed to determine the HLA-II risk alleles for developing Hashimoto's thyroiditis (HT) in order to analyze the molecular homology between candidate pathogen-derived epitopes and potentially self-antigens (thyroid peroxidase, TPO) based on the presence of HLA risk alleles. HLA-DRB1/-DQB1 genotyping was performed in 100 HT patients and 330 ethnically matched healthy controls to determine the predisposing/protective alleles for HT disease. Then, in silico analysis was conducted to examine the sequence homology between epitopes derived from autoantigens and four potentially relevant pathogens and their binding capacities to HLA risk alleles based on peptide docking analysis. We identified HLA-DRB1*03:01, *04:02, *04:05, and *11:04 as predisposing alleles and DRB1*13:01 as a potentially predictive allele for HT disease. Also, DRB1*11:04 ~ DQB1*03:01 (Pc = 0.002; OR, 3.97) and DRB1*03:01 ~ DQB1*02:01 (Pc = 0.004; OR, 2.24) haplotypes conferred a predisposing role for HT. Based on logistic regression analysis, carrying risk alleles increased the risk of HT development 4.5 times in our population (P = 7.09E-10). Also, ROC curve analysis revealed a high predictive power of those risk alleles for discrimination of the susceptible from healthy individuals (AUC, 0.70; P = 6.6E-10). Analysis of peptide sequence homology between epitopes of TPO and epitopes derived from four candidate microorganisms revealed a homology between envelop glycoprotein D of herpes virus and sequence 151-199 of TPO with remarkable binding capacity to HLA-DRB1*03:01 allele. Our findings indicate the increased risk of developing HT in those individuals carrying HLA risk alleles which can also be related to herpes virus infection.

Development and experimental validation of 3D QSAR models for the screening of thyroid peroxidase inhibitors using integrated methods of computational chemistry

The intricate network of glands and organs that makes up the endocrine system. Hormones are used to regulate and synchronize the nervous and physiological systems. The agents which perturbate an endocrine system are called endocrine disruptors and they can eventually affect cellular proliferation and differentiation in target tissues. A subclass of endocrine disruptors known as thyroid disruptors (TDs) or thyroid disrupting chemicals (TDCs) influence the hypothalamo-pituitary-thyroid axis or directly interfere with thyroid function by binding to thyroid hormone receptors. Thyroid hormone levels in circulation are now included in more test guidelines (OECD TG 441, 407, 408, 414, 421/422, 443/416). Although these might be adequate to recognize thyroid adversity, they are unable to explain the underlying mechanism of action. Thyroid peroxidase (TPO) and sodium iodide symporter (NIS), two proteins essential in the biosynthesis of thyroid hormones, are well-accepted molecular targets for inhibition. The screening of a large number of molecules using high throughput screening (HTS) requires a minimum quantity of sample, cost, and time consuming. Whereas 3-dimensional quantitative structure-activity relationship (3D-QSAR) analysis can screen the TDCs before synthesizing a compound. In the present study, the human TPO (hTPO) and NIS (hNIS) structures were modelled using homology modeling and the quality of the structures was validated satisfactorily using MD simulation for 100ns. Further, 190 human TPO inhibitors with IC50 were curated from Comptox and docked with the modelled structure of TPO using D238, H239 and D240 centric grid. The binding conformation of a molecule with low binding energy was used as a reference and the rest other molecules were aligned after generating the possible conformers. The activity-stratified partition was performed for aligned molecules and training set (139), test set (51) were defined. The machine learning models such as k Nearest Neighbor (kNN) and Random Forest (RF) models were built and validated using external experimental dataset containing 10 molecules. Among the 10 molecules, all 10 molecules were identified as TPO inhibitors and demonstrated 100 % accuracy qualitatively. To confirm the selective TPO inhibition all 10 molecules were docked with the modelled structure of hNIS and the results have demonstrated the selective TPO inhibition.

Disulfide Bonds of Thyroid Peroxidase Are Critical Elements for Subcellular Localization, Proteasome-Dependent Degradation, and Enzyme Activity

Background: Congenital hypothyroidism (CH) is caused by mutations in cysteine residues, including Cys655 and Cys825 that form disulfide bonds in thyroid peroxidase (TPO). It is highly likely that these disulfide bonds could play an important role in TPO activity. However, to date, no study has comprehensively analyzed cysteine mutations that form disulfide bonds in TPO. In this study, we induced mutations in cysteine residues involved in disulfide bonds formation and analyzed their effect on subcellular localization, degradation, and enzyme activities to evaluate the importance of disulfide bonds in TPO activity. Methods: Vector plasmid TPO mutants, C655F and C825R, known to occur in CH, were transfected into HEK293 cells. TPO activity and protein expression levels were measured by the Amplex red assay and Western blotting. The same procedure was performed in the presence of MG132 proteasome inhibitor. Subcellular localization was determined using immunocytochemistry and flow cytometry. The locations of all disulfide bonds within TPO were predicted using in silico analysis. All TPO mutations associated with disulfide bonds were induced. TPO activity and protein expression levels were also measured in all TPO mutants associated with disulfide bonds using the Amplex red assay and Western blotting. Results: C655F and C825R showed significantly decreased activity and protein expression compared with the wild type (WT) (p < 0.05). In the presence of the MG132 proteasome inhibitor, the protein expression level of TPO increased to a level comparable with that of the WT without increases in its activity. The degree of subcellular distribution of TPO to the cell surface in the mutants was lower compared with the WT TPO. Twenty-four cysteine residues were involved in the formation of 12 disulfide bonds in TPO. All TPO mutants harboring an amino acid substitution in each cysteine showed significantly reduced TPO activity and protein expression levels. Furthermore, the differences in TPO activity depended on the position of the disulfide bond. Conclusions: All 12 disulfide bonds play an important role in the activity of TPO. Furthermore, the mutations lead to misfolding, degradation, and membrane insertion.

Reactive Halogen Species: Role in Living Systems and Current Research Approaches

Reactive halogen species (RHS) are highly reactive compounds that are normally required for regulation of immune response, inflammatory reactions, enzyme function, etc. At the same time, hyperproduction of highly reactive compounds leads to the development of various socially significant diseases - asthma, pulmonary hypertension, oncological and neurodegenerative diseases, retinopathy, and many others. The main sources of (pseudo)hypohalous acids are enzymes from the family of heme peroxidases - myeloperoxidase, lactoperoxidase, eosinophil peroxidase, and thyroid peroxidase. Main targets of these compounds are proteins and peptides, primarily methionine and cysteine residues. Due to the short lifetime, detection of RHS can be difficult. The most common approach is detection of myeloperoxidase, which is thought to reflect the amount of RHS produced, but these methods are indirect, and the results are often contradictory. The most promising approaches seem to be those that provide direct registration of highly reactive compounds themselves or products of their interaction with components of living cells, such as fluorescent dyes. However, even such methods have a number of limitations and can often be applied mainly for in vitro studies with cell culture. Detection of reactive halogen species in living organisms in real time is a particularly acute issue. The present review is devoted to RHS, their characteristics, chemical properties, peculiarities of interaction with components of living cells, and methods of their detection in living systems. Special attention is paid to the genetically encoded tools, which have been introduced recently and allow avoiding a number of difficulties when working with living systems.