An Enzymatic Activity in Bovine Brain That Catalyzes the Reversal of the C-Terminal Methyl Esterification of Protein Phosphatase 2A

Abstract

A novel protein methyltransferase has been recently described that catalyzes the esterification of the C-terminal leucine residue of the catalytic subunit of protein phosphatase 2A in a variety of eucaryotic cells. This reaction can potentially modulate the phosphatase′s activity, subunit interactions, or interactions with specific phosphoprotein substrates. We present evidence here that the methylation reaction is reversible and that an enzymatic activity is present in bovine brain cytosol that catalyzes the hydrolysis of the methyl ester. We show that this activity is sensitive to inhibition by the serine-hydrolase inhibitor phenylmethanesulfonyl fluoride but is not affected by the small molecule substrate analog N-acetyl-L-leucine methyl ester. These results suggest that protein methylation and demethylation reactions can be utilized in eucaryotic cells to modulate enzyme activity in a parallel fashion to protein phosphorylation and dephosphorylation reactions.