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Mode of binding of the antithyroid drug propylthiouracil to mammalian haem peroxidases.

ABSTRACT: The mammalian haem peroxidase superfamily consists of myeloperoxidase (MPO), lactoperoxidase (LPO), eosinophil peroxidase (EPO) and thyroid peroxidase (TPO). These enzymes catalyze a number of oxidative reactions of inorganic substrates such as Cl(-), Br(-), I(-) and SCN(-) as well as of various organic aromatic compounds. To date, only structures of MPO and LPO are known. The substrate-binding sites in these enzymes are located on the distal haem side. Propylthiouracil (PTU) is a potent antithyroid drug that acts by inhibiting the function of TPO. It has also been shown to inhibit the action of LPO. However, its mode of binding to mammalian haem peroxidases is not yet known. In order to determine the mode of its binding to peroxidases, the structure of the complex of LPO with PTU has been determined. It showed that PTU binds to LPO in the substrate-binding site on the distal haem side. The IC50 values for the inhibition of LPO and TPO by PTU are 47 and 30?µM, respectively. A comparision of the residues surrounding the substrate-binding site on the distal haem side in LPO with those in TPO showed that all of the residues were identical except for Ala114 (LPO numbering scheme), which is replaced by Thr205 (TPO numbering scheme) in TPO. A threonine residue in place of alanine in the substrate-binding site may affect the affinity of PTU for peroxidases.

SUBMITTER: Singh RP

PROVIDER: S-EPMC4356306 | biostudies-literature | 2015 Mar

REPOSITORIES: biostudies-literature

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Mode of binding of the antithyroid drug propylthiouracil to mammalian haem peroxidases.

Singh R P RP Singh A A Kushwaha G S GS Singh A K AK Kaur P P Sharma S S Singh T P TP

Acta crystallographica. Section F, Structural biology communications 20150219 Pt 3

The mammalian haem peroxidase superfamily consists of myeloperoxidase (MPO), lactoperoxidase (LPO), eosinophil peroxidase (EPO) and thyroid peroxidase (TPO). These enzymes catalyze a number of oxidative reactions of inorganic substrates such as Cl(-), Br(-), I(-) and SCN(-) as well as of various organic aromatic compounds. To date, only structures of MPO and LPO are known. The substrate-binding sites in these enzymes are located on the distal haem side. Propylthiouracil (PTU) is a potent antithy ...[more]

PMID: 25760705

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Project description:Hyperthyroidism is a common endocrine disorder associated with increased risk of cardiovascular complications and mortality. Although antithyroid drugs (ATDs) are approved as first line option for many hyperthyroidism cases, including pregnancy and childhood, they exert significant toxic profile. Medicago sativa L. (alfalfa) also called "The father of all food" was among the diet consumed by mares that gave birth to foals with congenital hypothyroidism. Since, greenfeed was accused for the development of such condition, alfalfa may possess constituents with promising antithyroid potential that could be a valuable substitute for the conventional ATDs. The current work was designed to identify the most biologically active antithyroid phytoconstituent separated from alfalfa sprouts and comparing its antithyroid mechanism, efficacy and toxic profile to the standard ATD; propylthiouracil (PTU). The most biologically active solvent fractions from alfalfa sprouts extract were identified by in vitro screening for anti-thyroid peroxidase (TPO) activity, from which different phytoconstituents were separated and identified by interpretation of spectroscopic data. These compounds were then in vitro screened for anti-TPO and virtually screened via GLIDE XP docking into the crystal structures of the enzymes; bovine lactoperoxidase, as an alternative to TPO, and mammalian selenocysteine-dependent iodothyronine deiodinase (IDI), that are both uniquely dually prohibited by PTU. The compound that showed the least TPO IC50 and highest combined docking XP score was elected for comparing its antithyroid mechanism, efficacy, tendency to reverse hyperthyroidism-triggered complications and toxicity to PTU using L-thyroxine-induced hyperthyroidism model in rats. Seven compounds (1-7) were isolated from the most biologically active fraction, whilst, compounds (4-7) were reported for the first time from alfalfa sprouts. Compound 5 (apigenin) showed the least TPO IC50 and highest in-silico combined score, thus, apigenin was selected for further in-vivo investigations. Apigenin was found to more effectively interfere with type 1-IDI than with TPO in vivo. Apigenin therapy resulted in nearly euthyroid state, without incidence of hypothyroidism, thyroid hypertrophy, hepatotoxity or WBCs count reduction. In addition, apigenin, but not PTU, corrected hyperthyroidism-induced left ventricular hypertyrophy. Therefore, apigenin is a natural lead antithyroid drug that represents a possible safer alternative to conventional ATDs.

Dataset Information

Mode of binding of the antithyroid drug propylthiouracil to mammalian haem peroxidases.

Publications

Mode of binding of the antithyroid drug propylthiouracil to mammalian haem peroxidases.

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