Structures of SMG1-UPFs complexes: SMG1 contributes to regulate UPF2-dependent activation of UPF1 in NMD

Structure. 2014 Aug 5;22(8):1105-1119. doi: 10.1016/j.str.2014.05.015. Epub 2014 Jul 4.

Abstract

SMG1, a PI3K-related kinase, plays a critical role in nonsense-mediated mRNA decay (NMD) in mammals. SMG1-mediated phosphorylation of the UPF1 helicase is an essential step during NMD initiation. Both SMG1 and UPF1 are presumably activated by UPF2, but this regulation is incompletely understood. Here we reveal that SMG1C (a complex containing SMG1, SMG8, and SMG9) contributes to regulate NMD by recruiting UPF1 and UPF2 to distinct sites in the vicinity of the kinase domain. UPF2 binds SMG1 in an UPF1-independent manner in vivo, and the SMG1C-UPF2 structure shows UPF2 recognizes the FRB domain, a region that regulates the related mTOR kinase. The molecular architectures of several SMG1C-UPFs complexes, obtained by combining electron microscopy with in vivo and in vitro interaction analyses, competition experiments, and mutations, suggest that UPF2 can be transferred to UPF1 within SMG1C, inducing UPF2-dependent conformational changes required to activate UPF1 within an SMG1C-UPF1-UPF2 complex.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Blotting, Western
  • Enzyme Activation / physiology*
  • Humans
  • Image Processing, Computer-Assisted
  • Microscopy, Electron
  • Models, Molecular*
  • Multiprotein Complexes / genetics*
  • Multiprotein Complexes / metabolism
  • Nonsense Mediated mRNA Decay / genetics
  • Nonsense Mediated mRNA Decay / physiology*
  • Phosphatidylinositol 3-Kinases / chemistry*
  • Phosphatidylinositol 3-Kinases / metabolism
  • Phosphatidylinositol 3-Kinases / physiology
  • Phosphorylation
  • Protein Binding
  • Protein Conformation
  • Protein Serine-Threonine Kinases
  • RNA Helicases
  • RNA-Binding Proteins
  • Structure-Activity Relationship
  • Trans-Activators / chemistry*
  • Trans-Activators / metabolism
  • Transcription Factors / metabolism

Substances

  • Multiprotein Complexes
  • RNA-Binding Proteins
  • Trans-Activators
  • Transcription Factors
  • UPF2 protein, human
  • Protein Serine-Threonine Kinases
  • SMG1 protein, human
  • RNA Helicases
  • UPF1 protein, human