title: Structure of the protein core of translation initiation factor 2 in apo, GTP-bound and GDP-bound forms.
abstract: Translation initiation factor 2 (IF2) is involved in the early steps of bacterial protein synthesis. It promotes the stabilization of the initiator tRNA on the 30S initiation complex (IC) and triggers GTP hydrolysis upon ribosomal subunit joining. While the structure of an archaeal homologue (a/eIF5B) is known, there are significant sequence and functional differences in eubacterial IF2, while the trimeric eukaryotic IF2 is completely unrelated. Here, the crystal structure of the apo IF2 protein core from Thermus thermophilus has been determined by MAD phasing and the structures of GTP and GDP complexes were also obtained. The IF2-GTP complex was trapped by soaking with GTP in the cryoprotectant. The structures revealed conformational changes of the protein upon nucleotide binding, in particular in the P-loop region, which extend to the functionally relevant switch II region. The latter carries a catalytically important and conserved histidine residue which is observed in different conformations in the GTP and GDP complexes. Overall, this work provides the first crystal structure of a eubacterial IF2 and suggests that activation of GTP hydrolysis may occur by a conformational repositioning of the histidine residue.
authors.affiliation: Department of Integrated Structural Biology, IGBMC (Institute of Genetics and of Molecular and Cellular Biology), Centre National de la Recherche Scientifique (CNRS) UMR 7104/Institut National de la Santé de la Recherche Médicale (INSERM) U964/Université de Strasbourg, 1 Rue Laurent Fries, 67404 Illkirch, France.
authors.forename: Angelita
authors.initials: A
authors.lastname: Simonetti
authors.forename: Stefano
authors.initials: S
authors.lastname: Marzi
authors.forename: Attilio
authors.initials: A
authors.lastname: Fabbretti
authors.forename: Isabelle
authors.initials: I
authors.lastname: Hazemann
authors.forename: Lasse
authors.initials: L
authors.lastname: Jenner
authors.forename: Alexandre
authors.initials: A
authors.lastname: Urzhumtsev
authors.forename: Claudio O
authors.initials: CO
authors.lastname: Gualerzi
authors.forename: Bruno P
authors.initials: BP
authors.lastname: Klaholz
mesh_terms: D006153:Guanosine Diphosphate / Q000737:chemistry* / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008968:Molecular Conformation; D039881:Prokaryotic Initiation Factor-2 / Q000737:chemistry* / Q000378:metabolism; D016963:Thermus thermophilus / Q000737:chemistry* / Q000378:metabolism; D014961:X-Ray Diffraction
chemical_list: D039881:Prokaryotic Initiation Factor-2; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate
keywords: GDP; GTP; Thermus thermophilus; translation initiation factor 2