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Literature summary extracted from

  • Palioura, S.; Sherrer, R.L.; Steitz, T.A.; Sll, D.; Simonovic, M.
    The human SepSecS-tRNASec complex reveals the mechanism of selenocysteine formation (2009), Science, 325, 321-325.
    View publication on PubMedView publication on EuropePMC

Crystallization (Commentary)

EC Number Crystallization (Comment) Organism
2.9.1.2 crystal structure of the quaternary complex between human SepSecS, unacylated tRNASec, and a mixture of O-phosphoserine and thiophosphate to 2.8 A resolution Homo sapiens

Protein Variants

EC Number Protein Variants Comment Organism
2.9.1.2 K173A in vivo activity of the mutant is indistinguishable from that of the wild-type enzyme Homo sapiens
2.9.1.2 K173M in vivo activity of the mutant is indistinguishable from that of the wild-type enzyme Homo sapiens
2.9.1.2 Q105A mutant is inactive in vivo Homo sapiens
2.9.1.2 R313A mutant is inactive in vivo Homo sapiens
2.9.1.2 R75A mutant is inactive in vivo Homo sapiens
2.9.1.2 R97A in vivo activity of the mutant is indistinguishable from that of the wild-type enzyme Homo sapiens
2.9.1.2 R97Q in vivo activity of the mutant is indistinguishable from that of the wild-type enzyme Homo sapiens

Natural Substrates/ Products (Substrates)

EC Number Natural Substrates Organism Comment (Nat. Sub.) Natural Products Comment (Nat. Pro.) Rev. Reac.
2.9.1.2 L-phosphoseryl-tRNASec + selenophosphate Homo sapiens 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 L-selenocysteinyl-tRNASec + phosphate
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 ?

Organism

EC Number Organism UniProt Comment Textmining
2.9.1.2 Homo sapiens Q9HD40
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-

Reaction

EC Number Reaction Comment Organism Reaction ID
2.9.1.2 O-phospho-L-seryl-tRNASec + selenophosphate + H2O = L-selenocysteinyl-tRNASec + 2 phosphate 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
a

Substrates and Products (Substrate)

EC Number Substrates Comment Substrates Organism Products Comment (Products) Rev. Reac.
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 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
-
 ?

Subunits

EC Number Subunits Comment Organism
2.9.1.2 tetramer two SepSecS monomers form a homodimer, and two active sites are formed at the dimer interface. The two homodimers associate into a tetramer through interactions between the N-terminal alpha1-loop-alpha2 motifs Homo sapiens

Synonyms

EC Number Synonyms Comment Organism
2.9.1.2 O-phosphoseryl-tRNA:selenocysteinyl-tRNA synthase
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 Homo sapiens
2.9.1.2 SepSecS
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 Homo sapiens

Cofactor

EC Number Cofactor Comment Organism Structure
2.9.1.2 pyridoxal 5'-phosphate pyridoxal 5'-phosphate–dependent mechanism of Sec-tRNASec formation. Each SepSecS monomer has a pyridoxal 5'-phosphate cofactor covalently linked to the Nepsilon-amino group of the conserved Lys284 by means of formation of a Schiff base Homo sapiens