Structural determination of selenocysteine synthase complex (SelA) of Escherichia coli

Full text: The biosynthesis of the 21th amino acid, selenocysteine (Sec U), requires complex enzymatic machinery composed in eubacteria of: Selenocysteine Synthase (SELA), Selenocysteine Specific Elongation Factor (SELB), Selenophosphate Synthetase (SELD) and a specific Selenocysteine Inserting tRNA (tRNAsec). The Selenocysteine residue is incorporated into a nascent protein at a UGA like stop codon signaling as a Sec incorporation site by the presence of a Selenocysteine Insertion Sequence (SECIS), embedding the UGA codon in the coding region in bacteria and in a 3 UTR in archaea and eukarya. SELA plays a central role in this pathway by modifying the Serine residue charged into the tRNAsec by Seryl-tRNA Synthetase (SerRS) and converting it into Selenocysteine. This enzyme forms a homodecameric complex that specifically recognizes and binds to Seryl-tRNAsec. The specific interaction of SELA and its tRNA remains unclear. Our aim is the structural investigation by atomic force microscopy, negative staining and cryo-electronic microscopy of Escherichia coli SELA and SELA-tRNAsec. Microscopy data determined dimensional parameters as maximum dimension, molecular mass and radius of gyration. Recently study saw prospects of assuming one tRNA for monomeric protein of SELA, the models of AFM and cryo-microscopy may help to decide the number of tRNA interactions of SELA. (author)