title: Architecture of the eIF2B regulatory subcomplex and its implications for the regulation of guanine nucleotide exchange on eIF2.
abstract: Eukaryal translation initiation factor 2B (eIF2B) acts as guanine nucleotide exchange factor (GEF) for eIF2 and forms a central target for pathways regulating global protein synthesis. eIF2B consists of five non-identical subunits (α-ϵ), which assemble into a catalytic subcomplex (γ, ϵ) responsible for the GEF activity, and a regulatory subcomplex (α, β, δ) which regulates the GEF activity under stress conditions. Here, we provide new structural and functional insight into the regulatory subcomplex of eIF2B (eIF2B(RSC)). We report the crystal structures of eIF2Bβ and eIF2Bδ from Chaetomium thermophilum as well as the crystal structure of their tetrameric eIF2B(βδ)2 complex. Combined with mutational and biochemical data, we show that eIF2B(RSC) exists as a hexamer in solution, consisting of two eIF2Bβδ heterodimers and one eIF2Bα2 homodimer, which is homologous to homohexameric ribose 1,5-bisphosphate isomerases. This homology is further substantiated by the finding that eIF2Bα specifically binds AMP and GMP as ligands. Based on our data, we propose a model for eIF2B(RSC) and its interactions with eIF2 that is consistent with previous biochemical and genetic data and provides a framework to better understand eIF2B function, the molecular basis for Gcn(-), Gcd(-) and VWM/CACH mutations and the evolutionary history of the eIF2B complex.
authors.affiliation: Abteilung für Molekulare Strukturbiologie, Institut für Mikrobiologie und Genetik, Göttinger Zentrum für Molekulare Biowissenschaften, Georg-August-Universität Göttingen, D-37077 Göttingen, Germany bkuhle@gwdg.de.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Kuhle
authors.affiliation: Abteilung für Molekulare Strukturbiologie, Institut für Mikrobiologie und Genetik, Göttinger Zentrum für Molekulare Biowissenschaften, Georg-August-Universität Göttingen, D-37077 Göttingen, Germany.
authors.forename: Nora K
authors.initials: NK
authors.lastname: Eulig
authors.affiliation: Abteilung für Molekulare Strukturbiologie, Institut für Mikrobiologie und Genetik, Göttinger Zentrum für Molekulare Biowissenschaften, Georg-August-Universität Göttingen, D-37077 Göttingen, Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Ficner
mesh_terms: D002597:Chaetomium; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D020717:Eukaryotic Initiation Factor-2B / Q000737:chemistry* / Q000378:metabolism; D005656:Fungal Proteins / Q000737:chemistry* / Q000378:metabolism; D008024:Ligands; D008958:Models, Molecular; D055503:Protein Multimerization; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism
chemical_list: D015852:Eukaryotic Initiation Factor-2; D020717:Eukaryotic Initiation Factor-2B; D005656:Fungal Proteins; D008024:Ligands; D021122:Protein Subunits