TrxR

TRXR

Thioredoxin reductase (TrxR) is the main functional protein in the thioredoxin system and is widely found in many species from prokaryotes to mammals. TrxR is a member of the pyridine nucleotide/disulfide oxidoreductase family. TrxR mainly transfers electrons through redox reactions to relieve the body's oxidative stress response. It is the main way for the body to resist oxidative stress damage caused by internal and external factors. At the same time, it participates in various physiological processes such as carbohydrate synthesis, insulin production, fat metabolism, and the occurrence and development of chronic inflammation, tumors, atherosclerosis and other diseases.

Introductions

Thioredoxin (Trx) system is a ubiquitous disulfide reductase system in many species. It consists of thioredoxin (Trx), thioredoxin reductase (thioredoxinreducase, TrxR) and reduced coenzyme II composition. TrxR is currently the only enzyme known to reduce Trx, which regulates the dithiol/disulfide bond balance of proteins through disulfide bond reductase activity. Maintaining a dynamic balance between the reduction capacity of TrxR and oxidative stress is the key factor to ensure the normal body. Oxidative stress factors include superoxide ions, hydroxyl radicals, hydrogen peroxide and other reactive oxygen species. Reactive oxygen species (ROS) are usually present in all aerobic cells. The antioxidant system in the body forms a dynamic balance with endogenous or exogenous ROS. Once excess ROS is produced or antioxidants are depleted, the balance is destroyed and the body is damaged.

Structure of TrxR

TrxR belongs to the family of pyridine nucleotide disulfide oxidoreductases containing selenium, including the conserved-Cys-Val-Asn-Val-Gly-Cys-redox catalytic site and C-terminal-Cys-SeCys- (SeCys Is selenocysteine). The TrxR catalytic site is conservative in different species. As species have evolved from low to high levels, the structure and catalytic manner of TrxR have also changed. When the prokaryote TrxR disulfide ring is connected to the flavin surface, the disulfide is reduced and accompanied by oxidation of the flavin. However, the NADP (H) of TrxR is far away from the flavin ring, and the cysteine (disulfide) of the active site of NADP (H) is buried and cannot react with Trx. During the electron transfer process, NADP(H) rotates 67° towards the FAD domain, exposing the buried active site to the substrate, and finally transferring the electrons to the substrate and reducing the substrate.

Classification of TrxR

Different species of TrxR are distributed in different tissues, and their catalytic mechanisms are also different. These distributions and the different systems of different catalytic engines reflect the different evolution forms and evolutionary course of TrxR. TRXR is divided into two categories, namely, high molecular weight TrxR (H-TrxR) and low molecular weight TrxR (L-TrxR). H-TrxR has 3 domains, namely FAD domain, NADPH domain and C-terminal interface domain. H-TrxR C-terminal redox sequence is further divided into type Ⅰ and type Ⅱ. Type I TrxR refers to the X-Cys1-Cys2-X sequence with adjacent disulfide bonds. Type Ⅰ can be further divided into two subtypes: Type I TrxRs have a tetrapeptide C-terminal redox center of the GCUG sequence, where U is a rare amino acid, selenocysteine (SEC), such as human TrxR1 (NP-8773733 1) The C-terminal redox center is X-Cys1-Cys2sec-X; and the Sec residues in the tetrapeptide sequence of Ib-type TrxRS are replaced by conventional cysteine (Cys) residues [9], for example, human TrxR1 (2ZZ0-A) The C-terminal redox center is X-Cys1-Cys2-X. L-TrxR has two domains, only containing FAD and NADPH domains, but lacks the C-terminal interface.

Function of TrxR

By reducing Trx, TrxR achieves the purposes of reducing DNA, affecting selenium metabolism, anti-oxidation, regulating cell growth and regulating apoptosis, etc., affecting cell biological functions. The Trx/TrxR system plays an important role in physiological processes such as adipose tissue function, carbohydrate metabolism, insulin production and sensitivity, blood pressure regulation, inflammation, chemotactic activity of macrophages, and atherosclerosis. At the same time, due to the core role and diverse functions of the thioredoxin system in tumorigenesis and development, it has become one of the most attractive targets for tumor drug development.

Conclusion

TrxR is the main functional protein of the Trx system and participates in a wide range of biological activities from prokaryotes to mammals and other species. For the study of its structure and function, it can not only deepen the understanding of the evolution of species, but also accelerate the research and development of related disease treatment technologies. The structure of TrxR is an important basis for its biological function. Although the crystal structure of TrxR from prokaryotes to mammals has been partially resolved, in some species (Babesia), the structure and function of TrxR are not yet clear. Therefore, accelerating the research on the structure and function of TrxR of such species can expand human cognition of TrxR throughout the evolutionary history of organisms, and at the same time provide a theoretical basis for the prevention and control of such pathogens, as well as accelerate the development of targeted TrxR-related drugs.

Reference

1. Holmgren A. Thioredoxin and thioredoxin reductase: current research with special reference to human disease. Biochemical and Biophysical Research Communications. 2010, 396 (1): 120–4.