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B6db activities:
Description O-phospho-L-seryl-tRNA(Sec):L-selenocysteinyl-tRNA synthase
Alternative names L-phosphoseryl-tRNA(Ser):selenophosphate seleniumtransferase;
Sep (O-phosphoserine) tRNA:Sec (selenocysteine) tRNA synthase;
Sec synthase (ambiguous).
Catalyzed reaction O-phosphoseryl-tRNA(Sec) + Selenophosphate = L-Selenocysteinyl-tRNA(Sec) + Orthophosphate
Cofactor Pyridoxal phosphate
Comments A pyridoxal-phosphate protein. In archaea and eukarya selenocysteine formation is achieved by a two-step process: EC (O-phosphoseryl-tRNASec kinase) phosphorylates the endogenous L-seryl-tRNASec to O-phospho-L-seryl-tRNASec, and then this misacylated amino acid-tRNA species is converted to L-selenocysteinyl-tRNASec by Sep-tRNA:Sec-tRNA synthase.
This activity is specific of archaea and eukaryotes; these organisms synthesize L-selenocysteinyl-tRNA(Sec) from L-seryl-tRNA(Sec)trough a two-step pathway.
First, O-phosphoseryl-tRNA(Sec) kinase (PSTK) converts Ser-tRNA(Sec) to O-phosphoseryl-tRNA(Ser). This compound is then used as the substrate for Sep-tRNA:Sec-tRNA synthase (SepSecS).

In bacteria, L-seryl-tRNA(Sec) is directly converted to L-selenocysteinyl-tRNA(Sec) by EC (L-seryl-tRNA(Sec) selenium transferase).

Organisms -Archea -Metazoa -Human

Family (18)
Links Enzyme (activities)
BRENDA (activities)
KEGG (pathways)
PLPMDB (PLP mutants)
 Palioura S, Sherrer RL, Steitz TA, Söll D, Simonovic M. (2009) The human SepSecS-tRNASec complex reveals the mechanism of selenocysteine formation Science 325 321-5.

 Ganichkin OM, Xu XM, Carlson BA, Mix H, Hatfield DL, Gladyshev VN, Wahl MC. (2008) Structure and catalytic mechanism of eukaryotic selenocysteine synthase J Biol Chem 5849-65.

 Xu, X.M.; Carlson, B.A.; Mix, H.; Zhang, Y.; Saira K.; Glass, R.S.; Berry, M.J.; Gladyshev, V.N.; Hatfield, D.L. (2007) Biosynthesis of selenocysteine on its tRNA in eukaryotes PLoS Biol. e4.

 Yuan J, Palioura S, Salazar JC, Su D, O'Donoghue P, Hohn MJ, Cardoso AM, Whitman WB, Söll D. (2006) RNA-dependent conversion of phosphoserine forms selenocysteine in eukaryotes and archaea Proc Natl Acad Sci U S A 103 18923-7.

Articles on
last changed 2010/01/12 13:15

B6db activities