Structural and functional investigation of a putative archaeal selenocysteine synthaseKaiser, J.T., Gromadski, K., Rother, M., Engelhardt, H., Rodnina, M.V., Wahl, M.C.
(2005) Biochemistry 44: 13315-13327
- PubMed: 16201757
- DOI: 10.1021/bi051110r
- Primary Citation of Related Structures:
- PubMed Abstract:
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 fr ...
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.
Division of Chemistry and Chemical Engineering, California Institute of Technology, m/c 114-96, Pasadena, California 91125, USA.