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| {{STRUCTURE_2aev| PDB=2aev | SCENE= }} | | {{STRUCTURE_2aev| PDB=2aev | SCENE= }} |
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| '''MJ0158, NaBH4-reduced form'''
| | ===MJ0158, NaBH4-reduced form=== |
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| ==Overview==
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| Bacterial selenocysteine synthase converts seryl-tRNA(Sec) to selenocysteinyl-tRNA(Sec) for selenoprotein biosynthesis. The identity of this enzyme in archaea and eukaryotes is unknown. On the basis of sequence similarity, a conserved open reading frame has been annotated as a selenocysteine synthase gene in archaeal genomes. We have determined the crystal structure of the corresponding protein from Methanococcus jannaschii, MJ0158. The protein was found to be dimeric with a distinctive domain arrangement and an exposed active site, built from residues of the large domain of one protomer alone. The shape of the dimer is reminiscent of a substructure of the decameric Escherichia coli selenocysteine synthase seen in electron microscopic projections. However, biochemical analyses demonstrated that MJ0158 lacked affinity for E. coli seryl-tRNA(Sec) or M. jannaschii seryl-tRNA(Sec), and neither substrate was directly converted to selenocysteinyl-tRNA(Sec) by MJ0158 when supplied with selenophosphate. We then tested a hypothetical M. jannaschii O-phosphoseryl-tRNA(Sec) kinase and demonstrated that the enzyme converts seryl-tRNA(Sec) to O-phosphoseryl-tRNA(Sec) that could constitute an activated intermediate for selenocysteinyl-tRNA(Sec) production. MJ0158 also failed to convert O-phosphoseryl-tRNA(Sec) to selenocysteinyl-tRNA(Sec). In contrast, both archaeal and bacterial seryl-tRNA synthetases were able to charge both archaeal and bacterial tRNA(Sec) with serine, and E. coli selenocysteine synthase converted both types of seryl-tRNA(Sec) to selenocysteinyl-tRNA(Sec). These findings demonstrate that a number of factors from the selenoprotein biosynthesis machineries are cross-reactive between the bacterial and the archaeal systems but that MJ0158 either does not encode a selenocysteine synthase or requires additional factors for activity.
| | The line below this paragraph, {{ABSTRACT_PUBMED_16201757}}, adds the Publication Abstract to the page |
| | (as it appears on PubMed at http://www.pubmed.gov), where 16201757 is the PubMed ID number. |
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| | {{ABSTRACT_PUBMED_16201757}} |
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| ==About this Structure== | | ==About this Structure== |
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| [[Category: Pyridoxal phosphate]] | | [[Category: Pyridoxal phosphate]] |
| [[Category: Selenocysteine synthase]] | | [[Category: Selenocysteine synthase]] |
| ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sat May 3 18:57:42 2008'' | | |
| | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sun Jul 27 16:06:43 2008'' |
