Selenium Metabolism and Biosynthesis of Selenoproteins in the Human Body

Abstract

As an essential trace element, selenium (Se) plays a tremendous role in the functioning of the human organism being used for the biosynthesis of selenoproteins (proteins containing one or several selenocysteine residues). The functions of human selenoproteins in vivo are extremely diverse. Many selenoproteins have an antioxidant activity and, hence, play a key role in cell antioxidant defense and maintenance of redox homeostasis, which accounts for their involvement in diverse biological processes, such as signal transduction, proliferation, cell transformation and aging, ferroptosis, immune system functioning, etc. One of the critical functions of selenoenzymes is participation in the synthesis of thyroid hormones regulating basal metabolism in all body tissues. Over the last decades, optimization of population Se intake for prevention of diseases related to Se deficiency or excess has been recognized as a pressing issue in modern healthcare worldwide.

Keywords: antioxidants; selenium; selenocysteine; selenoproteins.

Fig. 1.

Metabolism of Se-containing compounds in human body. SeMet derived from plants is directly used for protein synthesis (1, SeMet cycle). Se released from SeMet and other compounds takes part in the Sec synthesis followed by the production of Sec-containing selenoproteins (2, selenoprotein cycle). H₂Se is one of the intermediates in the generation of Sec-tRNA^(Ser)Sec. Excessive Se is excreted from the body in the urine as trimethylselenonium ion and via respiratory tract in a form of dimethyl selenide. Se is also found in the urine in the content of selenosugars. Whether selenosugars take part in Se recirculation from the primary urine remains unknown.

Fig. 2.

Selenoprotein biosynthesis. First, Sec-tRNA^(Ser)Sec is produced in a three-stage process. Next, charged aminoacyl-tRNA in a complex with specific factors is transported to the free A-site of the ribosome that translates selenoprotein mRNA.