西亚试剂：The Human SepSecS-tRNASec Complex Reveals the Mechanism of

The Human SepSecS-tRNASec Complex Reveals the Mechanism of Selenocysteine Formation

Sotiria Palioura,1 R. Lynn Sherrer,1 Thomas A. Steitz,1,2,3 Dieter S?ll,1,2,* Miljan Simonovi4,*

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 tRNASec in complex with SepSecS, phosphoserine, and thiophosphate, together with in vivo and in vitro enzyme assays, supports a pyridoxal phosphate–dependent mechanism of Sec-tRNASec formation. Two tRNASec molecules, with a fold distinct from other canonical tRNAs, bind to each SepSecS tetramer through their 13–base pair acceptor-TC arm (where  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 tRNASec, but not free phosphoserine, to be oriented properly for the reaction to occur.

1 Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA.
2 Department of Chemistry, Yale University, New Haven, CT 06520, USA.
3 Howard Hughes Medical Institute, Yale University, New Haven, CT06520, USA.
4 Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, Chicago, IL 60607, USA.

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