Micronutrient Selenium: Uniqueness and Vital Functions

Abstract

Abstract—The trace element selenium, which was discovered by Berzelius in 1817, remains poorly investigated and exhibits diverse and surprising functions. We consider it unique for several reasons. First, it is present not only in organic or inorganic compounds but also in the amino acids selenocysteine and selenomethionine, as a key component, and in selenoproteins, which are found in all Domains of life. Second, selenocysteine is the 21st proteinogenic amino acid. Its uniqueness lies not only in the fact that it is encoded by one of the three stop codons of translation but in that its biosynthesis possesses unique features and that this process involves unique cis- and trans-active factors that are necessary for the recognition of this triplet as selenocysteine-encoding to avoid premature translation termination and synthesize full-sized selenoproteins. The maintenance of these cis- and trans-active factors is energy consuming, which suggests the crucial importance of selenoproteins for an organism. In addition, the pathways of amino-acid and selenoprotein biosynthesis have some distinctive features in different Domains of life. Third, the processes and effects of selenium compounds of different origins, in which this micronutrient plays key roles, are strikingly diverse, especially in the regulation of vital functions in mammals. This review uses the most recent data to present a comprehensive view of the properties and functions of selenium and to provide insight into the uniqueness of this micronutrient.