EC Number   |
Substrates |
Organism  |
Products |
Reversibility |
|---|
    2.9.1.2 | more |
Sep-tRNACys is converted by Sep-tRNA:Cys-tRNA synthase (SepCysS) to Cys-tRNACys |
Archaea |
? |
- |
- |
| 2.9.1.2 | O-phospho-L-seryl-tRNASec + selenophosphate + H2O |
- |
Archaea |
L-selenocysteinyl-tRNASec + 2 phosphate |
- |
? |
| 2.9.1.2 | more |
bacterial SepCysS charges bacterial tRNACys species with cysteine in vitro. Sep-tRNACys is converted by Sep-tRNA:Cys-tRNA synthase (SepCysS) to Cys-tRNACys |
Bacteria |
? |
- |
- |
| 2.9.1.2 | O-phospho-L-seryl-tRNASec + selenophosphate + H2O |
- |
Bacteria |
L-selenocysteinyl-tRNASec + 2 phosphate |
- |
? |
| 2.9.1.2 | L-phosphoseryl-tRNASec + selenophosphate |
selenocysteine is the only genetically encoded amino acid in humans whose biosynthesis occurs on its cognate transfer RNA (tRNA). O-Phosphoseryl-tRNA:selenocysteinyl-tRNA synthase catalyzes the final step of selenocysteine formation by a tRNA-dependent mechanism |
Homo sapiens |
L-selenocysteinyl-tRNASec + phosphate |
- |
? |
| 2.9.1.2 | more |
SepSecS binds unacylated tRNASec equally well as Sep-tRNASec 1 |
Homo sapiens |
? |
- |
- |
| 2.9.1.2 | O-phospho-L-seryl-tRNASec + selenophosphate |
- |
Homo sapiens |
L-selenocysteinyl-tRNASec + phosphate |
- |
? |
| 2.9.1.2 | O-phospho-L-seryl-tRNASec + selenophosphate |
L-phosphoseryl-tRNA is the crucial precursor for L-selenocysteinyl-tRNA formation in archaea and eukarya. Selenocysteine formation is achieved by a two-step process: 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 |
Homo sapiens |
L-selenocysteinyl-tRNASec + phosphate |
- |
? |
| 2.9.1.2 | O-phospho-L-seryl-tRNASec + selenophosphate |
proposed pyridoxal 5'-phosphate mechanism of L-phosphoseryl-tRNA to L-selenocysteinyl-tRNA conversion: the reaction begins by the covalently attached O-phospho-L-serine being brought into the proximity of the Schiff base when L-phosphoseryl-tRNASec binds to the enzyme. The amino group of O-phospho-L-serine can then attack the Schiff base formed between Lys284 and pyridoxal 5'-phosphate, which yields an external aldimine. The reoriented side chain of Lys284 abstracts the Calpha proton from O-phospho-L-serine, and the electron delocalization by the pyridine ring assists in rapid beta-elimination of the phosphate group, which produces an intermediate dehydroalanyl-tRNASec. After phosphate dissociation and binding of selenophosphate, the concomitant attack of water on the selenophosphate group and of the nucleophilic selenium onto the highly reactive dehydroalanyl moiety yield an oxidized form of L-phosphoseryl-tRNASec. The protonated Lys284, returns the proton to the Calpha carbon and then attacks pyridoxal 5'-phosphate to form an internal aldimine. Finally, Sec-tRNASec is released from the active site |
Homo sapiens |
L-selenocysteinyl-tRNASec + phosphate |
- |
? |
| 2.9.1.2 | O-phospho-L-seryl-tRNASec + selenophosphate + H2O |
- |
Homo sapiens |
L-selenocysteinyl-tRNASec + 2 phosphate |
- |
? |
