title: Importance of the beta12-beta13 loop in protein phosphatase-1 catalytic subunit for inhibition by toxins and mammalian protein inhibitors.
abstract: Type-1 protein serine/threonine phosphatases (PP1) are uniquely inhibited by the mammalian proteins, inhibitor-1 (I-1), inhibitor-2 (I-2), and nuclear inhibitor of PP1 (NIPP-1). In addition, several natural compounds inhibit both PP1 and the type-2 phosphatase, PP2A. Deletion of C-terminal sequences that included the beta12-beta13 loop attenuated the inhibition of the resulting PP1alpha catalytic core by I-1, I-2, NIPP-1, and several toxins, including tautomycin, microcystin-LR, calyculin A, and okadaic acid. Substitution of C-terminal sequences from the PP2A catalytic subunit produced a chimeric enzyme, CRHM2, that was inhibited by toxins with dose-response characteristics of PP1 and not PP2A. However, CRHM2 was insensitive to the PP1-specific inhibitors, I-1, I-2, and NIPP-1. The anticancer compound, fostriecin, differed from other phosphatase inhibitors in that it inhibited wild-type PP1alpha, the PP1alpha catalytic core, and CRHM2 with identical IC(50). Binding of wild-type and mutant phosphatases to immobilized microcystin-LR, NIPP-1, and I-2 established that the beta12-beta13 loop was essential for the association of PP1 with toxins and the protein inhibitors. These studies point to the importance of the beta12-beta13 loop structure and conformation for the control of PP1 functions by toxins and endogenous proteins.
authors.affiliation: Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710, USA.
authors.forename: J H
authors.initials: JH
authors.lastname: Connor
authors.forename: T
authors.initials: T
authors.lastname: Kleeman
authors.forename: S
authors.initials: S
authors.lastname: Barik
authors.forename: R E
authors.initials: RE
authors.lastname: Honkanen
authors.forename: S
authors.initials: S
authors.lastname: Shenolikar
mesh_terms: D000475:Alkenes / Q000494:pharmacology; D000595:Amino Acid Sequence; D000935:Antifungal Agents / Q000494:pharmacology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D052998:Microcystins; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010456:Peptides, Cyclic / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000235:genetics; D011090:Polyenes; D011485:Protein Binding; D054645:Protein Phosphatase 1; D017433:Protein Structure, Secondary; D011506:Proteins / Q000494:pharmacology; D011714:Pyrans; D011753:Pyrones; D017386:Sequence Homology, Amino Acid; D013141:Spiro Compounds; D000097847:Protein Phosphatase Inhibitory Proteins
chemical_list: D000475:Alkenes; D000935:Antifungal Agents; D004791:Enzyme Inhibitors; D052998:Microcystins; D010456:Peptides, Cyclic; D010749:Phosphoprotein Phosphatases; D011090:Polyenes; D054645:Protein Phosphatase 1; D011506:Proteins; D011714:Pyrans; D011753:Pyrones; D013141:Spiro Compounds; C024833:protein phosphatase inhibitor-2; D000097847:Protein Phosphatase Inhibitory Proteins; C053079:tautomycin; C078588:microcystin; C040313:fostriecin