Fluorescence studies on the interaction of inhibitor 2 and okadaic acid with the catalytic subunit of type 1 phosphoprotein phosphatases. |
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Authors: | W D Picking W Kudlicki G Kramer B Hardesty J R Vandenheede W Merlevede I K Park A DePaoli-Roach |
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Institution: | Department of Chemistry and Biochemistry, University of Texas, Austin 78712. |
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Abstract: | Phosphatase inhibitor 2 was mutagenized and expressed in Escherichia coli to produce a protein with a single cysteinyl residue at position 129. The newly introduced sulfhydryl group was labeled with a maleimide derivative of coumarin (CPM). The resulting fluorescent inhibitor 2 molecule (CPM-I2) retains biological activity and binds to the catalytic subunit of type 1 phosphatase (PP1-C) with a Kd similar to the Ki of native I2 (2-3 nM). Fluorescence anisotropy data indicate that kinase FA (glycogen synthase kinase 3) does not dissociate the CPM-I2.PP1-C complex but rather causes a conformational change in the I2 molecule that is retained even after the CPM-I2 is displaced by an excess of native I2. The fluorescence data presented here also indicate that okadaic acid and I2 are competitive for binding to PP1-C, even after kinase FA treatment of the CPM-I2.PP1-C complex. |
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