title: Analysis of the subunit organization of the eIF2B complex reveals new insights into its structure and regulation.
abstract: Eukaryotic initiation factor 2B (eIF2B) is the guanine nucleotide exchange factor for eIF2 and a critical regulator of protein synthesis, (e.g., as part of the integrated stress response). Certain mutations in the EIF2B genes cause leukoencephalopathy with vanishing white matter (VWM), an often serious neurological disorder. Comprising 5 subunits, α-ε (eIF2Bε being the catalytic one), eIF2B has always been considered an αβγδε heteropentamer. We have analyzed the subunit interactions within mammalian eIF2B by using a combination of mass spectrometry and in vivo studies of overexpressed complexes to gain further insight into the subunit arrangement of the complex. Our data reveal that eIF2B is actually decameric, a dimer of eIF2B(βγδε) tetramers stabilized by 2 copies of eIF2Bα. We also demonstrate a pivotal role for eIF2Bδ in the formation of eIF2B(βγδε) tetramers. eIF2B(αβγδε)2 decamers show greater binding to eIF2 than to eIF2B(βγδε) tetramers, which may underlie the increased activity of the former. We examined the levels of eIF2B subunits in a panel of different mouse tissues and identified different levels of eIF2B subunits, particularly eIF2Bα, which implies heterogeneity in the cellular proportions of eIF2B(αβγδε) and eIF2B(βγδε) complexes, with important implications for the regulation of translation in individual cell types.
authors.affiliation: 1University of Southampton, Centre for Biological Sciences; Life Sciences Building 85, Highfield Campus, Southampton SO17 1BJ, UK. n.c.wortham@soton.ac.uk.
authors.forename: Noel C
authors.initials: NC
authors.lastname: Wortham
authors.forename: Magdalena
authors.initials: M
authors.lastname: Martinez
authors.forename: Yuliya
authors.initials: Y
authors.lastname: Gordiyenko
authors.forename: Carol V
authors.initials: CV
authors.lastname: Robinson
authors.forename: Christopher G
authors.initials: CG
authors.lastname: Proud
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002384:Catalysis; D003593:Cytoplasm / Q000378:metabolism; D020717:Eukaryotic Initiation Factor-2B / Q000737:chemistry* / Q000378:metabolism; D005786:Gene Expression Regulation; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D013058:Mass Spectrometry; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D040901:Proteomics; D011994:Recombinant Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D020717:Eukaryotic Initiation Factor-2B; D011994:Recombinant Proteins
keywords: protein synthesis; vanishing white matter