Mn2+ is a native metal ion activator for bacteriophage λ protein phosphatase

Bacteriophage A protein phosphatase (lambdaPP) is a member of a large family of metal-containing phosphoesterases, including purple acid phosphatase, protein serine/threonine phosphatases, 5'-nucleotidase, and DNA repair enzymes such as Mre11. lambdaPP can be activated several-fold by various divalent metal ions, with Mn2+ and Ni2+ providing the most significant activation. Despite the extensive characterization of purified lambdaPP in vitro, little is known about the identity and stoichiometry of metal ions used by lambdaPP in vivo. In this report, we describe the use of metal analysis, activity measurements, and whole cell EPR spectroscopy to investigate in vivo metal binding and activation of lambdaPP. Escherichia coli cells overexpressing lambdaPP show a 22.5-fold increase in intracellular Mn concentration and less dramatic changes in the intracellular concentration of other biologically relevant metal ions compared to control cells that do not express lambdaPP. Phosphatase activity assessed using para-nitrophenylphosphate as substrate is increased 850-fold in cells overexpressing lambdaPP, indicating the presence of metal-activated enzyme in cell lysate. EPR spectra of intact cells overexpressing lambdaPP exhibit resonances previously attributed to mononuclear Mn2+ and dinuclear [(Mn2+)(2)] species bound to lambdaPP. Spin quantitation of EPR spectra of intact E. coli cells overexpressing lambdaPP indicates the presence of approximately 40 muM mononuclear Mn2+-lambdaPP and 60 muM [(Mn2+)(2)]-lambdaPP. The data suggest that overexpression of lambdaPP results in a mixture of apo-, mononuclear-Mn2+, and dinuclear-[(Mn2+)(2)] metalloisoforms and that Mn2+ is a physiologically relevant activating metal ion in E. coli.