Protein phosphatase 2C (PP2C) family is characterized by requirement of
metal cation for
phosphatase activity. We previously established that PPM1H is a
cancer-associated member of the PP2C family. Here we further characterized the
phosphatase activity of PPM1H, focusing on its dependence on
metal cation. PPM1H possesses the potential to dephosphorylate
p-nitrophenyl phosphate (
pNPP),
casein and
phosphopeptides. Interestingly, PPM1H shows the
metal preference that is varied depending on the substrate (substrate-dependent
metal preference); PPM1H prefers Mn(2+) when
pNPP or
phosphopeptides is used as a substrate. Meanwhile, a preference for Mg(2+) is displayed by PPM1H with
casein as a substrate. When both
cations are added to the reaction, the degree of the effect is always closer to that with Mn(2+) alone, irrespective of the substrate. This preponderance of Mn(2+) is explained by its greater affinity for PPM1H than Mg(2+). From the literature the substrate-dependent
metal preference appears to be shared by other PP2Cs. According to the crystal structure, a binuclear
metal center of PP2C plays an important role for coordinating the substrate and nucleophilic waters in the active site. Therefore, the differences in the size, preferred geometry and coordination requirements between two metals, in relation to the substrate, may be responsible for this intriguing property.