Studies on the activation of isocitrate dehydrogenase kinase/phosphatase (AceK) by Mn2+ and Mg2+

Isocitrate dehydrogenase kinase/phosphatase (AceK) is a bifunctional enzyme with both kinase and phosphatase activities that are activated by Mg2+. We have studied the interactions of Mn(2+)and Mg2+ with AceK using isothermal titration calorimetry (ITC) combined with molecular docking simulations and show for the first time that Mn2+ also activates the enzyme activities. However, Mn2+ and Mg2+ exert their effects by different mechanisms. Although they have similar binding constants (of 1.11x10(5) and 0.98x10(5)M(-1), respectively) for AceK and induce conformational changes of the enzyme, they do not compete for the same binding site. Instead Mn2+ appears to bind to the regulatory domain of AceK, and its effect is transmitted to the active site of the enzyme by the conformational change that it induces. The information in this study should be very useful for understanding the molecular mechanism underlying the interaction between AceK and metal ions, especially Mn2+ and Mg2+.