title: Repair of isoaspartate formation modulates the interaction of deamidated 4E-BP2 with mTORC1 in brain.
abstract: In eukaryotes, a rate-limiting step of translation initiation is recognition of the mRNA 5' m(7)GpppN cap structure by the eukaryotic initiation factor 4F (eIF4F), a heterotrimeric complex consisting of the cap-binding protein, eIF4E, along with eIF4G, and eIF4A. The eIF4E-binding proteins (4E-BPs) repress translation by disrupting eIF4F formation, thereby preventing ribosome recruitment to the mRNA. Of the three 4E-BPs, 4E-BP2 is the predominant paralog expressed in the mammalian brain and plays an important role in synaptic plasticity and learning and memory. 4E-BP2 undergoes asparagine deamidation, solely in the brain, during early postnatal development. Deamidation spontaneously converts asparagines into a mixture of aspartates or isoaspartates, the latter of which may be destabilizing to proteins. The enzyme protein L-isoaspartyl methyltransferase (PIMT) prevents isoaspartate accumulation by catalyzing the conversion of isoaspartates to aspartates. PIMT exhibits high activity in the brain, relative to other tissues. We report here that 4E-BP2 is a substrate for PIMT. In vitro deamidated 4E-BP2 accrues isoapartyl residues and is methylated by recombinant PIMT. Using an antibody that recognizes 4E-BP2, which harbors isoaspartates at the deamidation sites, Asn(99) and Asn(102), we demonstrate that 4E-BP2 in PIMT-/- brain lysates contains isoaspartate residues. Further, we show that 4E-BP2 containing isoaspartates lacks the augmented association with raptor that is a feature of deamidated 4E-BP2.
authors.affiliation: Department of Biochemistry and Goodman Cancer Centre, McGill University, Montréal, Québec H3G 1Y6, Canada.
authors.forename: Michael
authors.initials: M
authors.lastname: Bidinosti
authors.forename: Yvan
authors.initials: Y
authors.lastname: Martineau
authors.forename: Filipp
authors.initials: F
authors.lastname: Frank
authors.forename: Nahum
authors.initials: N
authors.lastname: Sonenberg
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001921:Brain / Q000378:metabolism*; D002384:Catalysis; D039642:Eukaryotic Initiation Factors / Q000737:chemistry*; D006801:Humans; D026581:Isoaspartic Acid / Q000737:chemistry*; D000076222:Mechanistic Target of Rapamycin Complex 1; D008745:Methylation; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes; D011485:Protein Binding; D014176:Protein Biosynthesis; D011506:Proteins; D011994:Recombinant Proteins / Q000737:chemistry; D012436:S-Adenosylmethionine / Q000737:chemistry; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors / Q000737:chemistry*
chemical_list: C104151:EIF4EBP2 protein, human; D039642:Eukaryotic Initiation Factors; D026581:Isoaspartic Acid; D046912:Multiprotein Complexes; D011506:Proteins; D011994:Recombinant Proteins; D014157:Transcription Factors; D012436:S-Adenosylmethionine; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases