Abstract
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 (SepSecS) catalyzes the final step of selenocysteine formation by a poorly understood tRNA-dependent mechanism. The crystal structure of human tRNA(Sec) in complex with SepSecS, phosphoserine, and thiophosphate, together with in vivo and in vitro enzyme assays, supports a pyridoxal phosphate-dependent mechanism of Sec-tRNA(Sec) formation. Two tRNA(Sec) molecules, with a fold distinct from other canonical tRNAs, bind to each SepSecS tetramer through their 13-base pair acceptor-TPsiC arm (where Psi indicates pseudouridine). The tRNA binding is likely to induce a conformational change in the enzyme's active site that allows a phosphoserine covalently attached to tRNA(Sec), but not free phosphoserine, to be oriented properly for the reaction to occur.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, Non-P.H.S.
MeSH terms
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Amino Acyl-tRNA Synthetases / chemistry*
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Amino Acyl-tRNA Synthetases / metabolism*
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Base Sequence
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Biocatalysis
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Catalytic Domain
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Crystallography, X-Ray
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Humans
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Hydrogen Bonding
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Models, Molecular
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Molecular Sequence Data
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Nucleic Acid Conformation
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Phosphates / chemistry
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Phosphates / metabolism
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Phosphoserine / chemistry
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Phosphoserine / metabolism
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Protein Conformation
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Protein Multimerization
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Protein Structure, Secondary
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RNA, Transfer, Amino Acid-Specific / chemistry*
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RNA, Transfer, Amino Acid-Specific / metabolism*
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RNA, Transfer, Amino Acyl / metabolism*
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Selenocysteine / biosynthesis*
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Selenocysteine / genetics
Substances
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Phosphates
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RNA, Transfer, Amino Acid-Specific
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RNA, Transfer, Amino Acyl
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selenocysteinyl-tRNA
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tRNA, selenocysteine-
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Selenocysteine
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Phosphoserine
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Amino Acyl-tRNA Synthetases
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O-phosphoseryl-tRNA:selenocysteinyl-tRNA synthase, human
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thiophosphoric acid