Reversible oxidation controls the activity and oligomeric state of the mammalian phosphoglycolate phosphatase AUM.

Redox-dependent switches of enzyme activity are emerging as important fine-tuning mechanisms in cell signaling. For example, protein tyrosine phosphatases employ a conserved cysteine residue for catalysis, which also renders them highly susceptible to reversible inactivation by oxidation. In contrast, haloacid dehalogenase (HAD)-type phosphatases perform catalysis via a phosphoaspartyltransferase reaction. The potential regulation of HAD phosphatases by reversible oxidation has not yet been explored. Here, we investigate the redox-sensitivity of the HAD-type phosphoglycolate phosphatase PGP, also known as AUM or glycerol-3-phosphate phosphatase. We show that recombinant, purified murine PGP is inhibited by oxidation and re-activated by reduction. We identify three reactive cysteine residues in the catalytic core domain of PGP (Cys35, Cys104 and Cys243) that mediate the reversible inhibition of PGP activity and the associated, redox-dependent conformational changes. Structural analysis suggests that Cys35 oxidation weakens van-der-Waals interactions with Thr67, a conserved catalytic residue required for substrate coordination. Cys104 and Cys243 form a redox-dependent disulfide bridge between the PGP catalytic core and cap domains, which may impair the open/close-dynamics of the catalytic cycle. In addition, we demonstrate that Cys297 in the PGP cap domain is essential for redox-dependent PGP oligomerization, and that PGP oxidation/oligomerization occurs in response to stimulation of cells with EGF. Finally, employing a modified cysteinyl-labeling assay, we show that cysteines of cellular PGP are transiently oxidized to sulfenic acids. Taken together, our findings establish that PGP, an aspartate-dependent HAD phosphatase, is transiently inactivated by reversible oxidation in cells.

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