PMID: 19608919 , Related PDB id: 3HL2

Authors:

Palioura S, Sherrer RL, Steitz TA, Soll D, Simonovic M

Title:

The human SepSecS-tRNASec complex reveals the mechanism of selenocysteine formation.

Journal:

Science. 2009 Jul 17;325(5938):321-5.

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.