title: Structure of translation initiation factor 5A from Pyrobaculum aerophilum at 1.75 A resolution.
abstract: BACKGROUND
  Translation initiation factor 5A (IF-5A) is reported to be involved in the first step of peptide bond formation in translation, to be involved in cell-cycle regulation and to be a cofactor for the Rev and Rex transactivator proteins of human immunodeficiency virus-1 and T-cell leukemia virus I, respectively. IF-5A contains an unusual amino acid, hypusine (N-epsilon-(4-aminobutyl-2-hydroxy)lysine), that is required for its function. The first step in the post-translational modification of lysine to hypusine is catalyzed by the enzyme deoxyhypusine synthase, the structure of which has been published recently.
  
  
  RESULTS
  IF-5A from the archebacterium Pyrobaculum aerophilum has been heterologously expressed in Escherichia coli with selenomethionine substitution. The crystal structure of IF-5A has been determined by multiwavelength anomalous diffraction and refined to 1.75 A. Unmodified P. aerophilum IF-5A is found to be a beta structure with two domains and three separate hydrophobic cores.
  
  
  CONCLUSIONS
  The lysine (Lys42) that is post-translationally modified by deoxyhypusine synthase is found at one end of the IF-5A molecule in an turn between beta strands beta4 and beta5; this lysine residue is freely solvent accessible. The C-terminal domain is found to be homologous to the cold-shock protein CspA of E. coli, which has a well characterized RNA-binding fold, suggesting that IF-5A is involved in RNA binding.
authors.affiliation: Life Sciences Division Los Alamos National Laboratory Mail Stop M888, Los Alamos, New Mexico, 87545, USA peat@proi1.lanl.gov
authors.forename: T S
authors.initials: TS
authors.lastname: Peat
authors.forename: J
authors.initials: J
authors.lastname: Newman
authors.forename: G S
authors.initials: GS
authors.lastname: Waldo
authors.forename: J
authors.initials: J
authors.lastname: Berendzen
authors.forename: T C
authors.initials: TC
authors.lastname: Terwilliger
mesh_terms: D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D018360:Crystallography, X-Ray; D019641:DNA, Archaeal / Q000737:chemistry; D004926:Escherichia coli; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D010448:Peptide Initiation Factors / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure*; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D016601:RNA-Binding Proteins; D016415:Sequence Alignment; D055672:Static Electricity; D019624:Thermoproteaceae / Q000737:chemistry* / Q000235:genetics; D000097574:Eukaryotic Translation Initiation Factor 5A
chemical_list: D019641:DNA, Archaeal; D010448:Peptide Initiation Factors; D016601:RNA-Binding Proteins; D000097574:Eukaryotic Translation Initiation Factor 5A; C115531:aIF-5A