| Type: | Family | Name: | Selenophosphate synthetase |
| Description: | The UGA (TGA) codon is normally a termination codon, however it is also used as a selenocysteine (Sec) codon by numerous organisms []. Sec is the 21st amino acid that is inserted into selenoproteins (protein that includes a selenocysteine (Se-Cys) amino acid residue). The synthesis of Sec and its incorporation into proteins requires the activity of a number of proteins, one of which is selenophosphate synthetase (SPS), also known as the SelD gene product [, ]. SPS catalises the production of the selenium donor compound monoselenophosphate (MSP) from selenide and ATP. MSP is then used to synthesize Sec from seryl-tRNAs []. SPS was initially identified in E. coli as the product of the gene selD, one of four essential selenoprotein synthesis genes (selA-D) []. SelC is the tRNA itself, SelD acts as a donor of reduced selenium, SelA modifies a serine residue on SelC into selenocysteine, and SelB is a selenocysteine-specific translation elongation factor. 3' or 5' non-coding elements of mRNA have been found as probable structures for directing selenocysteine incorporation. Later, the selD homologues from eukaryotes, bacteria, and archaea were identified [].In mammals, two gene products, SPS1 and SPS2 are proposed to be selenophosphate synthetases. SPS1 may be involved in Sec recycling via a selenium salvage pathway, whereas SPS2 may play a role in the synthesis of selenophosphate []. SPS2 is a selenoprotein and could serve as an autoregulator of selenoprotein synthesis []. Drosophila SPS1 (UniProt: O18373) lacks selenide-dependent SPS activity due to an arginine substitution of the critical Cys (or Sec) residue in the catalytic domain of the enzyme when expressed in E. coli []. Drosophila SPS2 (also known as Dsps2) is a selenoprotein that contains a UGA stop codon in the catalytic centre of the enzyme, nevertheless, the read-through activity can be provided by a mammalian-like SECIS element in its 3'UTR []. | Short Name: | SPS/SelD |
