title: Structure of the Elongator cofactor complex Kti11/Kti13 provides insight into the role of Kti13 in Elongator-dependent tRNA modification.
abstract: Modification of wobble uridines of many eukaryotic tRNAs requires the Elongator complex, a highly conserved six-subunit eukaryotic protein assembly, as well as the Killer toxin-insensitive (Kti) proteins 11-14. Kti11 was additionally shown to be implicated in the biosynthesis of diphthamide, a post-translationally modified histidine of translation elongation factor 2. Recent data indicate that iron-bearing Kti11 functions as an electron donor to the [4Fe-4S] cluster of radical S-Adenosylmethionine enzymes, triggering the subsequent radical reaction. We show here that recombinant yeast Kti11 forms a stable 1 : 1 complex with Kti13. To obtain insights into the function of this heterodimer, the Kti11/Kti13 complex was purified to homogeneity, crystallized, and its structure determined at 1.45 Å resolution. The importance of several residues mediating complex formation was confirmed by mutagenesis. Kti13 adopts a fold characteristic of RCC1-like proteins. The seven-bladed β-propeller consists of a unique mixture of four- and three-stranded blades. In the complex, Kti13 orients Kti11 and restricts access to its electron-carrying iron atom, constraining the electron transfer capacity of Kti11. Based on these findings, we propose a role for Kti13, and discuss the possible functional implications of complex formation.
  
  
  METHODS
  Structural data have been submitted to the Protein Data Bank under accession number 4X33.
authors.affiliation: Equipe Labellisée La Ligue, Institut de Génétique et de Biologie Moléculaire et Cellulaire, Centre National de Recherche Scientifique UMR 7104/Institut National de Santé et de Recherche Médicale U964/Université de Strasbourg, Illkirch, France.
authors.forename: Olga
authors.initials: O
authors.lastname: Kolaj-Robin
authors.forename: Alastair G
authors.initials: AG
authors.lastname: McEwen
authors.forename: Jean
authors.initials: J
authors.lastname: Cavarelli
authors.forename: Bertrand
authors.initials: B
authors.lastname: Séraphin
mesh_terms: D001665:Binding Sites; D018360:Crystallography, X-Ray; D004579:Electron Transport; D007501:Iron / Q000737:chemistry; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D012343:RNA, Transfer / Q000737:chemistry / Q000378:metabolism*; D012097:Repressor Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D055672:Static Electricity
chemical_list: C089099:ATS1 protein, S cerevisiae; C459979:KTI11 protein, S cerevisiae; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D012343:RNA, Transfer; D007501:Iron
keywords: Kti11/Kti13; Saccharomyces cerevisiae; electron transfer; elongator; tRNA modification