Toward understanding phosphoseryl-tRNACys formation: the crystal structure of Methanococcus maripaludis phosphoseryl-tRNA synthetase.
Publication Type:Journal Article
Source:Proc Natl Acad Sci U S A, Volume 104, Issue 8, p.2620-5 (2007)
Keywords:Adenosine Triphosphate, Amino Acid Sequence, Amino Acyl-tRNA Synthetases, Binding Sites, Crystallography, X-Ray, Diphosphates, Kinetics, Methanococcus, Models, Molecular, Molecular Sequence Data, Mutant Proteins, Phosphoserine, Protein Structure, Quaternary, Protein Structure, Secondary, Protein Structure, Tertiary, RNA, Transfer, Cys, Structural Homology, Protein, Thermus thermophilus
<p>A number of archaeal organisms generate Cys-tRNA(Cys) in a two-step pathway, first charging phosphoserine (Sep) onto tRNA(Cys) and subsequently converting it to Cys-tRNA(Cys). We have determined, at 3.2-A resolution, the structure of the Methanococcus maripaludis phosphoseryl-tRNA synthetase (SepRS), which catalyzes the first step of this pathway. The structure shows that SepRS is a class II, alpha(4) synthetase whose quaternary structure arrangement of subunits closely resembles that of the heterotetrameric (alphabeta)(2) phenylalanyl-tRNA synthetase (PheRS). Homology modeling of a tRNA complex indicates that, in contrast to PheRS, a single monomer in the SepRS tetramer may recognize both the acceptor terminus and anticodon of a tRNA substrate. Using a complex with tungstate as a marker for the position of the phosphate moiety of Sep, we suggest that SepRS and PheRS bind their respective amino acid substrates in dissimilar orientations by using different residues.</p>