An international study has been highlighted on the cover of the prestigious journal Genome Research. It illustrates the evolution of selenophosphate synthetase genes —involved in selenoprotein synthesis— in prokaryotic and eukaryotic organisms. Montserrat Corominas and Florenci Serras, professors in the Department of Genetics and researchers at the Institute of Biomedicine of the University of Barcelona (IBUB), participate in the study together with the scientific team led by Roderic Guigó, expert at the Centre for Genomic Regulation (CRG-UPF).
A map of the evolutionary history of selenoproteins
Selenoproteins are proteins that incorporate selenocysteine, a nonstandard amino acid which is analogous to cysteine (also known as the 21st amino acid) but contains a dietary element: selenium. Selenium is an essential nutrient in diet even if it is a scarce element. In fact, it is a key element in many metabolic pathways and both its abundance and deficiency can cause some problems. To be exact, selenocysteine (Sec) has a structure similar to cysteine but it contains an atom of selenium instead of an atom of sulphur.
Selenocysteine synthesis and insertion requires the intervention of several factors: a specific transfer RNA, RNA and ribosome binding proteins, a specific elongation factor, and the enzyme selenophosphate synthetase (SPS). The study describes the evolutionary history of SPS genes and provides a functional map of selenoprotein function spanning the whole tree of life.
Duplicated genes with different evolutionary patterns
SPS is itself a selenoprotein in many species, although functionally equivalent homologs that replace the Sec site with cysteine (Cys) are common. Many metazoans, however, possess SPS genes with substitutions other than Sec or Cys (collectively referred to as SPS1).
The study highlights that SPS1 genes originated through a number of independent gene duplications from an ancestral metazoan selenoprotein SPS2 gene that most likely already carried the SPS1 function. During evolution, SPS2 gene duplicates in several metazoans in an independent way, and generates a new protein (SPS1), in which Sec has been replaced by an amino acid different from cysteine (for example, arginine in insects, threonine in vertebrates or glycine in ascidians).
Complementation assays in Drosophila mutants suggest that these genes share a common function, which appears to be distinct from the synthesis of selenophosphate carried out by the Sec- and Cys- SPS genes (termed SPS2). This evolutionary history constitutes a remarkable example of emergence and evolution of gene function, wherein the amino acid at a single site determines unequivocally protein function.
Image: The study developed by experts at the University of Barcelona and the Centre for Genomic Regulation is on the cover of the journal Genome Research
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