The role of the autoinhibitory domain in differential metal ion activation of calmodulin-stimulated phosphatase

Metal ion activators, Ni²⁺ and Mn²⁺, have been suggested to induce different conformations of calmodulin (CaM)-stimulated phosphatase. In the present study, an autoinhibitory domain previously implicated in the conformation transition of CaM stimulation of the phosphatase is shown to participate in defining the differential metal ion activation. A proteolytic derivative of the phosphatase deleted from the autoinhibitory domain displayed CaM-independent Mn²⁺-stimulated activity which was about 4-times that of the CaM-stimulated activity of the native enzyme. The Ni²⁺-stimulated activity of the derivative, on the other hand, retained slight CaM-dependence, and the CaM-stimulated activity was 90% of that of the native enzyme. A synthetic peptide corresponding to the autoinhibitory domain could inhibit the Mn²⁺-stimulated activity of the phosphatase derivative by 80%, but had little effect on the Ni²⁺-stimulated activity.