Title: Protein Factors Mediating Selenoprotein SynthesisĪuthor(s): Alain Lescure, Delphine Fagegaltier, Philippe Carbon and Alain Krol Keywords: Selenoprotein Synthesis, phospholipid hydroperoxide, selb translation factors, secis-binding proteins, glutathione peroxidase phgpx In this review, we will focus on the structural and functional aspects of the SelB and SBP2 factors in selenoprotein synthesis. Obviously, selenoprotein synthesis represents a higher degree of complexity than anticipated, and more needs to be discovered in eukaryotes. As a consequence, an important difference between the eubacterial and eukaryal selenoprotein synthesis machineries is that the functions of SelB are divided into two proteins in eukaryotes. The role is carried out by SBP2 that also forms a protein-protein complex with mSelB / EFSec. In contrast to the eubacterial SelB, the specialized elongation factor mSelB / EFSec the SECIS RNA binding function. Indeed, the discovery of the SECIS RNA binding protein SBP2, which is not a translation factor, paved the way for the subsequent isolation of mSelB / EFSec, the mammalian homolog of SelB. In the last couple of years, remarkable progress has been made toward understanding the underlying mecha nism in mammals. In archaea and eukaryotes, selenocysteine incorporation exhibits a higher degree of complexity because the SECIS hairpin is localized in the 3 untranslated region of the mRNA. SelB is thus a bifunctional factor, carrying functional homology to elongation factor EF-Tu in its N-terminal domain and SECIS RNA binding activity via its C-terminal extension.

SelB conveys the Sec-tRNASec to the A site of the ribosome through binding to the SECIS mRNA hairpin adjacent to the UGA Sec codon.

To decode the UGA Sec codon in eubacteria, this machinery comprises the tRNASec, the specialized elongation factor SelB and the SECIS hairpin in the selenoprotein mRNAs. Both the synthesis of selenocysteine and its co-translational incorporation into selenoproteins in response to an in-frame UGA codon, require a complex molecular machinery. The amino acid selenocysteine represents the major biological form of selenium.

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