Domains of phosphatase inhibitor-2 involved in the control of the ATP-Mg- dependent protein phosphatase

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Inhibitor-2 (1-2) inhibits the free catalytic subunit of type 1 phosphatase (CS1) and controls the cyclic inactivation/activation of CS1 in the ATP-Mg-dependent protein phosphatase complex. We report here the effect of mutations on these two properties of 1-2. Substitution of Thr-72 with Ala, Asp, or Glu generated complexes with CS1 that could not be activated. Mutation of Ser-86 did not affect activation by glycogen synthase kinase-3 (GSK-3) alone but impaired synergistic activation by casein kinase II and GSK-3. Mutations in the region between Thr-72 and Ser-86 did not alter the inhibitory potency of 1-2 but prevented complete inactivation of CS1. A mutant without the 35 NH2-terminal residues exhibited an IC50 for CS1 200-fold higher than that of wild-type 1-2. However, it formed an inactive phosphatase complex with CS1, which was activated by GSK-3. A mutant with the 59 COOH-terminal residues deleted retained full inhibitory activity and formed an inactive complex that could not be activated by GSK-3. We conclude that the NH2-terminal region of 1-2 is involved in inhibition, that the sequence between Thr-72 and Ser-86 is necessary for the conversion of CS1 from an active to an inactive conformation, and that the COOH terminus is required for activation by GSK-3. Thus, different functional domains of 1-2 may interact with distinct regions of CS1.

Original languageEnglish (US)
Pages (from-to)28919-28928
Number of pages10
JournalJournal of Biological Chemistry
Issue number46
StatePublished - Jan 1 1994

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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