Journal
SCIENCE
Volume 325, Issue 5938, Pages 321-325Publisher
AMER ASSOC ADVANCEMENT SCIENCE
DOI: 10.1126/science.1173755
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Funding
- DOE
- NIGMS
- HHMI, Yale University
- Yale University School of Medicine MD/PhD Program
- Ruth L. Kirschstein National Research Service Award
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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-T Psi C 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.
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