title: Purification and properties of Arabidopsis thaliana type 1 protein phosphatase (PP1).
abstract: The Arabidopsis thaliana type 1 protein phosphatase (PP1) catalytic subunit was released from its endogenous regulatory subunits by ethanol precipitation and purified by anion exchange and microcystin affinity chromatography. The enzyme was identified by MALDI-TOF mass spectrometry from a tryptic digest of the purified protein as a mixture of PP1 isoforms (TOPP 1-6) indicating that at least 4-6 of the eight known PP1 proteins are expressed in sufficient quantities for purification from A. thaliana suspension cells. The enzyme had a final specific activity of 8950 mU/mg using glycogen phosphorylase a as substrate, had a subunit molecular mass of 35 kDa as determined by SDS-PAGE and behaved as a monomeric protein of approx. 39 kDa on Superose 12 gel filtration chromatography. Similar to the mammalian type 1 protein phosphatases, the A. thaliana enzyme was potently inhibited by Inhibitor-2 (IC(50)=0.65 nM), tautomycin (IC(50)=0.06 nM), microcystin-LR (IC(50)=0.01 nM), nodularin (IC(50)=0.035 nM), calyculin A (IC(50)=0.09 nM), okadaic acid (IC(50)=20 nM) and cantharidin (IC(50)=60 nM). The enzyme was also inhibited by fostriecin (IC(50)=22 microM), NaF (IC(50)=2.1 mM), Pi (IC(50)=9.5 mM), and PPi (IC(50)=0.07 mM). Purification of the free catalytic subunit allowed it to be used to probe protein phosphatase holoenzyme complexes that were enriched on Q-Sepharose and a microcystin-Sepharose affinity matrix and confirmed several proteins to be PP1 targeting subunits.
authors.affiliation: Department of Biological Sciences, University of Calgary, AB, Canada.
authors.forename: M D
authors.initials: MD
authors.lastname: Stubbs
authors.forename: H T
authors.initials: HT
authors.lastname: Tran
authors.forename: A J
authors.initials: AJ
authors.lastname: Atwell
authors.forename: C S
authors.initials: CS
authors.lastname: Smith
authors.forename: D
authors.initials: D
authors.lastname: Olson
authors.forename: G B
authors.initials: GB
authors.lastname: Moorhead
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000737:chemistry / Q000201:enzymology*; D002846:Chromatography, Affinity; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D004591:Electrophoresis, Polyacrylamide Gel; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000302:isolation & purification*; D010936:Plant Extracts / Q000737:chemistry; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D004791:Enzyme Inhibitors; D010446:Peptide Fragments; D010936:Plant Extracts; D010749:Phosphoprotein Phosphatases