Specificity of different isoforms of protein phosphatase‐2A and protein phosphatase‐2C studied using site‐directed mutagenesis of HMG‐CoA reductase

Abstract

We have expressed the catalytic domain of Chinese hamster HMG‐CoA reductase, and 13 point mutations involving the region around the single phosphorylation site for AMP‐activated protein kinase. After phosphorylation, these were used to test the specificity of isoforms of protein phosphatase‐2A [bovine PP2A_C (catalytic subunit) and PP2A₁ (ABC heterotrimer)] and protein phosphatase‐2C (human α; mouse α, β1, β2, β3, β4, β5). PP2A₁ had >50‐fold higher activity for HMG‐CoA reductase variants than PP2A_C, but their relative selectivity for different variants was similar. Although the specificities of PP2A and PP2C were distinct, no dramatic differences in selectivity were observed between different PP2C isoforms.