The predicted β12-β13 loop is important for inhibition of PP2Acα by the antitumor drug fostriecin

Abstract
The potential anticancer agent fostriecin (FOS) is a potent inhibitor of the protein Ser/Thr phosphatases PP2A and PP4 and a weaker inhibitor of PP1. Random mutagenesis and automated screening in yeast identified residues in human PP2Acα important for inhibitory FOS binding. A C269S substitution in the predicted β12–β13 loop decreased the FOS sensitivity of intact cells and increased the IC50 of PP2Acα by 10-fold in vitro. Changing PP2Acα Cys-269 to phenylalanine, the equivalent residue in PP1, and the Y267G and G270D substitutions caused a similar effect. The results provide information relevant to the design of novel protein Ser/Thr phosphatase inhibitory drugs

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