title: Identification and characterization of AtI-2, an Arabidopsis homologue of an ancient protein phosphatase 1 (PP1) regulatory subunit.
abstract: PP1 (protein phosphatase 1) is among the most conserved enzymes known, with one or more isoforms present in all sequenced eukaryotic genomes. PP1 dephosphorylates specific serine/threonine phosphoproteins as defined by associated regulatory or targeting subunits. In the present study we performed a PP1-binding screen to find putative PP1 interactors in Arabidopsis thaliana and uncovered a homologue of the ancient PP1 interactor, I-2 (inhibitor-2). Bioinformatic analysis revealed remarkable conservation of three regions of plant I-2 that play key roles in binding to PP1 and regulating its function. The sequence-related properties of plant I-2 were compared across eukaryotes, indicating a lack of I-2 in some species and the emergence points from key motifs during the evolution of this ancient regulator. Biochemical characterization of AtI-2 (Arabidopsis I-2) revealed its ability to inhibit all plant PP1 isoforms and inhibitory dependence requiring the primary interaction motif known as RVXF. Arabidopsis I-2 was shown to be a phosphoprotein in vivo that was enriched in the nucleus. TAP (tandem affinity purification)-tag experiments with plant I-2 showed in vivo association with several Arabidopsis PP1 isoforms and identified other potential I-2 binding proteins.
authors.affiliation: Department of Biological Sciences, University of Calgary, 2500 University Drive, Calgary, Alberta, T2N 1N4, Canada.
authors.forename: George W
authors.initials: GW
authors.lastname: Templeton
authors.forename: Mhairi
authors.initials: M
authors.lastname: Nimick
authors.forename: Nicholas
authors.initials: N
authors.lastname: Morrice
authors.forename: David
authors.initials: D
authors.lastname: Campbell
authors.forename: Marilyn
authors.initials: M
authors.lastname: Goudreault
authors.forename: Anne-Claude
authors.initials: AC
authors.lastname: Gingras
authors.forename: Atsushi
authors.initials: A
authors.lastname: Takemiya
authors.forename: Ken-Ichiro
authors.initials: K
authors.lastname: Shimazaki
authors.forename: Greg B G
authors.initials: GB
authors.lastname: Moorhead
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D019295:Computational Biology / Q000379:methods; D030562:Databases, Protein; D008969:Molecular Sequence Data; D010750:Phosphoproteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D010802:Phylogeny; D019441:Plant Epidermis / Q000166:cytology / Q000378:metabolism; D018515:Plant Leaves / Q000166:cytology / Q000378:metabolism; D018514:Plant Structures / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D054645:Protein Phosphatase 1 / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D029681:Arabidopsis Proteins; D010750:Phosphoproteins; D020033:Protein Isoforms; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins; C558185:AtI-2 protein, Arabidopsis; D054645:Protein Phosphatase 1