title: Phosphorylation of S776 and 14-3-3 binding modulate ataxin-1 interaction with splicing factors.
abstract: Ataxin-1 (Atx1), a member of the polyglutamine (polyQ) expanded protein family, is responsible for spinocerebellar ataxia type 1. Requirements for developing the disease are polyQ expansion, nuclear localization and phosphorylation of S776. Using a combination of bioinformatics, cell and structural biology approaches, we have identified a UHM ligand motif (ULM), present in proteins associated with splicing, in the C-terminus of Atx1 and shown that Atx1 interacts with and influences the function of the splicing factor U2AF65 via this motif. ULM comprises S776 of Atx1 and overlaps with a nuclear localization signal and a 14-3-3 binding motif. We demonstrate that phosphorylation of S776 provides the molecular switch which discriminates between 14-3-3 and components of the spliceosome. We also show that an S776D Atx1 mutant previously designed to mimic phosphorylation is unsuitable for this aim because of the different chemical properties of the two groups. Our results indicate that Atx1 is part of a complex network of interactions with splicing factors and suggest that development of the pathology is the consequence of a competition of aggregation with native interactions. Studies of the interactions formed by non-expanded Atx1 thus provide valuable hints for understanding both the function of the non-pathologic protein and the causes of the disease.
authors.affiliation: National Institute for Medical Research, Medical Research Council, London, United Kingdom.
authors.forename: Cesira
authors.initials: C
authors.lastname: de Chiara
authors.forename: Rajesh P
authors.initials: RP
authors.lastname: Menon
authors.forename: Molly
authors.initials: M
authors.lastname: Strom
authors.forename: Toby J
authors.initials: TJ
authors.lastname: Gibson
authors.forename: Annalisa
authors.initials: A
authors.lastname: Pastore
mesh_terms: D048948:14-3-3 Proteins / Q000378:metabolism*; D017398:Alternative Splicing / Q000235:genetics; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000067696:Ataxin-1; D000067528:Ataxins; D001667:Binding, Competitive; D002151:Calorimetry; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000378:metabolism*; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism*; D010455:Peptides / Q000737:chemistry; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism*; D011485:Protein Binding; D012261:Ribonucleoproteins / Q000378:metabolism*; D020539:Sequence Analysis, Protein; D017386:Sequence Homology, Amino Acid; D000072668:Splicing Factor U2AF
chemical_list: D048948:14-3-3 Proteins; C000593749:ATXN1 protein, human; D000067696:Ataxin-1; D000067528:Ataxins; D050505:Mutant Proteins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D010455:Peptides; D010750:Phosphoproteins; D012261:Ribonucleoproteins; D000072668:Splicing Factor U2AF; C000607494:U2AF2 protein, human; D010768:Phosphoserine