title: The cyanobacterial toxin microcystin binds covalently to cysteine-273 on protein phosphatase 1.
abstract: The interaction between protein phosphatase 1 (PP1) and microcystin (MC) was stable in 1% SDS or 70% formic acid indicative of a covalent interaction. Here we isolate the MC-binding peptide and demonstrate that Cys273 of PP1 binds covalently to the methyl-dehydroalanine (Mdha) residue of the toxin. Mutation of Cys273 to Ala, Ser or Leu abolished covalent binding to MC, as did reduction of the Mdha residue of the toxin with ethanethiol. The abolition of covalent binding increased the IC50 for toxin inhibition of PP1 by 5- to 20-fold. The covalent binding of MC to protein serine/threonine phosphatases explains the failure to detect this toxin post-mortem in suspected cases of MC poisoning.
authors.affiliation: Department of Biochemistry, University of Dundee, Scotland, UK.
authors.forename: R W
authors.initials: RW
authors.lastname: MacKintosh
authors.forename: K N
authors.initials: KN
authors.lastname: Dalby
authors.forename: D G
authors.initials: DG
authors.lastname: Campbell
authors.forename: P T
authors.initials: PT
authors.lastname: Cohen
authors.forename: P
authors.initials: P
authors.lastname: Cohen
authors.forename: C
authors.initials: C
authors.lastname: MacKintosh
mesh_terms: D000409:Alanine / Q000031:analogs & derivatives / Q000378:metabolism; D000595:Amino Acid Sequence; D001427:Bacterial Toxins / Q000378:metabolism*; D001483:Base Sequence; D000458:Cyanobacteria / Q000378:metabolism*; D003545:Cysteine / Q000378:metabolism*; D006801:Humans; D007457:Iodine Radioisotopes; D007553:Isotope Labeling; D052998:Microcystins; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010455:Peptides; D010456:Peptides, Cyclic / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D011485:Protein Binding; D054645:Protein Phosphatase 1
chemical_list: D001427:Bacterial Toxins; D007457:Iodine Radioisotopes; D052998:Microcystins; D010455:Peptides; D010456:Peptides, Cyclic; C078588:microcystin; C015102:dehydroalanine; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D003545:Cysteine; D000409:Alanine