title: Structural insights into the second step of RNA-dependent cysteine biosynthesis in archaea: crystal structure of Sep-tRNA:Cys-tRNA synthase from Archaeoglobus fulgidus.
abstract: In the ancient organisms, methanogenic archaea, lacking the canonical cysteinyl-tRNA synthetase, Cys-tRNA(Cys) is produced by an indirect pathway, in which O-phosphoseryl-tRNA synthetase ligates O-phosphoserine (Sep) to tRNA(Cys) and Sep-tRNA:Cys-tRNA synthase (SepCysS) converts Sep-tRNA(Cys) to Cys-tRNA(Cys). In this study, the crystal structure of SepCysS from Archaeoglobus fulgidus has been determined at 2.4 A resolution. SepCysS forms a dimer, composed of monomers bearing large and small domains. The large domain harbors the seven-stranded beta-sheet, which is typical of the pyridoxal 5'-phosphate (PLP)-dependent enzymes. In the active site, which is located near the dimer interface, PLP is covalently bound to the side-chain of the conserved Lys209. In the proximity of PLP, a sulfate ion is bound by the side-chains of the conserved Arg79, His103, and Tyr104 residues. The active site is located deep within the large, basic cleft to accommodate Sep-tRNA(Cys). On the basis of the surface electrostatic potential, the amino acid residue conservation mapping, the position of the bound sulfate ion, and the substrate amino acid binding manner in other PLP-dependent enzymes, a binding model of Sep-tRNA(Cys) to SepCysS was constructed. One of the three strictly conserved Cys residues (Cys39, Cys42, or Cys247), of one subunit may play a crucial role in the catalysis in the active site of the other subunit.
authors.affiliation: Department of Biophysics and Biochemistry, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Ryuya
authors.initials: R
authors.lastname: Fukunaga
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Yokoyama
mesh_terms: D000595:Amino Acid Sequence; D000604:Amino Acyl-tRNA Synthetases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D019843:Archaeal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D019611:Archaeoglobus fulgidus / Q000201:enzymology*; D001665:Binding Sites; D018360:Crystallography, X-Ray; D003545:Cysteine / Q000096:biosynthesis*; D019281:Dimerization; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D020836:Protein Structure, Quaternary; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012313:RNA / Q000378:metabolism; D012346:RNA, Transfer, Amino Acyl / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D055672:Static Electricity; D013431:Sulfates / Q000378:metabolism
chemical_list: D019843:Archaeal Proteins; D021122:Protein Subunits; D012346:RNA, Transfer, Amino Acyl; D013431:Sulfates; D012313:RNA; D000604:Amino Acyl-tRNA Synthetases; D003545:Cysteine