title: Structure of the AlaX-M trans-editing enzyme from Pyrococcus horikoshii.
abstract: The editing domain of alanyl-tRNA synthetase (AlaRS) contributes to high-fidelity aminoacylation by hydrolyzing (editing) the incorrect products Ser-tRNA(Ala) and Gly-tRNA(Ala) (cis-editing). The AlaX protein shares sequence homology to the editing domain of AlaRS. There are three types of AlaX proteins, with different numbers of amino-acid residues (AlaX-S, AlaX-M and AlaX-L). In this report, AlaX-M from Pyrococcus horikoshii is shown to deacylate Ser-tRNA(Ala) and Gly-tRNA(Ala) (trans-editing). The crystal structure of P. horikoshii AlaX-M has been determined at 2.7 A resolution. AlaX-M consists of an N-terminal domain (N-domain) and a C-terminal domain (C-domain). A zinc ion is coordinated by the conserved zinc-binding cluster in the C-domain, which is expected to be the enzymatic active site. The glycine-rich motif, consisting of successive conserved glycine residues in the N-domain, forms a loop (the 'glycine-rich loop'). The glycine-rich loop is located near the active site and may be involved in substrate recognition and/or catalysis.
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: D000412:Alanine-tRNA Ligase / Q000737:chemistry* / Q000378:metabolism; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001665:Binding Sites; D002413:Cations, Divalent; D018360:Crystallography, X-Ray; D005998:Glycine / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D043902:Pyrococcus horikoshii / Q000201:enzymology*; D017393:RNA Editing; D012353:RNA, Transfer, Gly / Q000737:chemistry; D012362:RNA, Transfer, Ser / Q000737:chemistry; D016415:Sequence Alignment; D015032:Zinc / Q000378:metabolism
chemical_list: D002413:Cations, Divalent; D012353:RNA, Transfer, Gly; D012362:RNA, Transfer, Ser; D000412:Alanine-tRNA Ligase; D015032:Zinc; D005998:Glycine