Expanding the repertoire of the eukaryotic selenoproteome

Abstract

Selenium, an essential trace element known primarily for its antioxidant properties, exerts a diversity of functions through its presence in selenoproteins, proteins in which selenium is incorporated into the nascent polypeptide cotranslationally by means of the amino acid selenocysteine (Sec). Although the function of many selenoprotein families is unknown, the importance of selenoprotein synthesis has been clearly demonstrated in animals, in which mutations that render the cell unable to incorporate selenium into proteins result in embryonic lethality (1). With few exceptions, characterized selenoprotein families are known to function enzymatically and are typically involved in redox reactions. In these selenoprotein families, the Sec residue is found in the active site of the enzyme. Because nearly all eukaryotic selenoproteins are represented within mammalian genomes, mammals have been thought to recapitulate the eukaryotic selenoproteome, the set of all selenoproteins. However, by using bioinformatic approaches, Castellano et al. (2) have identified and characterized a fish selenoprotein family, SelJ, that challenges these paradigms. Their findings, published in this issue of PNAS, reinforce the seemingly universal importance of selenium by showing the vast and diverse phylogenetic distributions of selenoproteins across taxa. Selenoprotein translation relies on …