Evolutionary Basis for the Use of Selenocysteine
Evolutionary adaptations to dietary selenium may explain the use of selenocysteine in proteins. If so, adaptive signals should be present in the genomic regions of selenoprotein genes. It is, however, difficult to identify the signatures of adaptation left by natural selection in the genome of extant species (including humans). Furthermore, dietary adaptations to selenium may have happened in some species but not in others. For example, while dietary selenium does not seem to be a major selective force behind the evolution of selenocysteine use in vertebrate proteins, it may be an important factor in other lineages. Whether levels of selenium in the diet have driven the evolution of other functionally important amino acid changes in selenoproteins is not known. Dietary selenium may have also shaped the regulation of selenoprotein genes and of genes involved in the metabolism of selenium. Evolutionary genetics methods aimed at detecting signals of natural selection at the regulatory level are key to answering this question. Understanding the genetic basis of adaptations to levels of selenium in the diet would help shed light on the molecular mechanisms behind the metabolism of selenium.
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