title: Structural and functional analysis of the three MIF4G domains of nonsense-mediated decay factor UPF2.
abstract: Nonsense-mediated decay (NMD) is a eukaryotic quality control pathway, involving conserved proteins UPF1, UPF2 and UPF3b, which detects and degrades mRNAs with premature stop codons. Human UPF2 comprises three tandem MIF4G domains and a C-terminal UPF1 binding region. MIF4G-3 binds UPF3b, but the specific functions of MIF4G-1 and MIF4G-2 are unknown. Crystal structures show that both MIF4G-1 and MIF4G-2 contain N-terminal capping helices essential for stabilization of the 10-helix MIF4G core and that MIF4G-2 interacts with MIF4G-3, forming a rigid assembly. The UPF2/UPF3b/SMG1 complex is thought to activate the kinase SMG1 to phosphorylate UPF1 in vivo. We identify MIF4G-3 as the binding site and in vitro substrate of SMG1 kinase and show that a ternary UPF2 MIF4G-3/UPF3b/SMG1 complex can form in vitro. Whereas in vivo complementation assays show that MIF4G-1 and MIF4G-2 are essential for NMD, tethering assays reveal that UPF2 truncated to only MIF4G-3 and the UPF1-binding region can still partially accomplish NMD. Thus UPF2 MIF4G-1 and MIF4G-2 appear to have a crucial scaffolding role, while MIF4G-3 is the key module required for triggering NMD.
authors.affiliation: European Molecular Biology Laboratory, Grenoble Outstation, 6 rue Jules Horowitz, 38042 Grenoble Cedex 9, France, Unit of Virus Host-Cell Interactions, University of Grenoble Alpes-EMBL-CNRS, UMI 3265, 6 rue Jules Horowitz, 38042 Grenoble Cedex 9, France and University of Cologne, Institute for Genetics, Zuelpicher Street 47a, 50674 Cologne, Germany.
authors.forename: Marcello
authors.initials: M
authors.lastname: Clerici
authors.forename: Aurélien
authors.initials: A
authors.lastname: Deniaud
authors.forename: Volker
authors.initials: V
authors.lastname: Boehm
authors.forename: Niels H
authors.initials: NH
authors.lastname: Gehring
authors.forename: Christiane
authors.initials: C
authors.lastname: Schaffitzel
authors.forename: Stephen
authors.initials: S
authors.lastname: Cusack
mesh_terms: D006367:HeLa Cells; D006801:Humans; D008958:Models, Molecular; D059365:Nonsense Mediated mRNA Decay; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D016601:RNA-Binding Proteins / Q000378:metabolism; D014157:Transcription Factors / Q000737:chemistry* / Q000378:metabolism
chemical_list: D016601:RNA-Binding Proteins; D014157:Transcription Factors; C468286:UPF2 protein, human; D019869:Phosphatidylinositol 3-Kinases