3bc8
From Proteopedia
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'''Crystal structure of mouse selenocysteine synthase''' | '''Crystal structure of mouse selenocysteine synthase''' | ||
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[[Category: Transferase]] | [[Category: Transferase]] | ||
[[Category: X-ray crystallography]] | [[Category: X-ray crystallography]] | ||
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Revision as of 17:37, 4 May 2008
Crystal structure of mouse selenocysteine synthase
Overview
In eukaryotes and Archaea, selenocysteine synthase (SecS) converts O-phospho-l-seryl-tRNA([Ser]Sec) into selenocysteyl-tRNA([Ser]Sec) using selenophosphate as the selenium donor compound. The molecular mechanisms underlying SecS activity are presently unknown. We have delineated a 450-residue core of mouse SecS, which retained full selenocysteyl-tRNA([Ser]Sec) synthesis activity, and determined its crystal structure at 1.65A resolution. SecS exhibits three domains that place it in the fold type I family of pyridoxal phosphate (PLP)-dependent enzymes. Two SecS monomers interact intimately and together build up two identical active sites around PLP in a Schiff-base linkage with lysine 284. Two SecS dimers further associate to form a homotetramer. The N terminus, which mediates tetramer formation, and a large insertion that remodels the active site set SecS aside from other members of the family. The active site insertion contributes to PLP binding and positions a glutamate next to the PLP, where it could repel substrates with a free alpha-carboxyl group, suggesting why SecS does not act on free O-phospho-l-serine. Upon soaking crystals in phosphate buffer, a previously disordered loop within the active site insertion contracted to form a phosphate binding site. Residues that are strictly conserved in SecS orthologs but variant in related enzymes coordinate the phosphate and upon mutation corrupt SecS activity. Modeling suggested that the phosphate loop accommodates the gamma-phosphate moiety of O-phospho-l-seryl-tRNA([Ser]Sec) and, after phosphate elimination, binds selenophosphate to initiate attack on the proposed aminoacrylyl-tRNA([Ser]Sec) intermediate. Based on these results and on the activity profiles of mechanism-based inhibitors, we offer a detailed reaction mechanism for the enzyme.
About this Structure
3BC8 is a Single protein structure of sequence from Mus musculus. Full crystallographic information is available from OCA.
Reference
Structure and catalytic mechanism of eukaryotic selenocysteine synthase., Ganichkin OM, Xu XM, Carlson BA, Mix H, Hatfield DL, Gladyshev VN, Wahl MC, J Biol Chem. 2008 Feb 29;283(9):5849-65. Epub 2007 Dec 19. PMID:18093968 Page seeded by OCA on Sun May 4 20:37:31 2008
