Involved in the degradation of aromatic compounds via the protocatechuate 4,5-cleavage pathway (PubMed:11495993). Catalyzes the hydrolysis of 2-pyrone-4,6-dicarboxylate (PDC) to oxalomesaconate (OMA) (PubMed:7142106). Also catalyzes the reverse reaction (PubMed:7142106). 2-oxo-2H-pyran-4,6-dicarboxylate + H2O = (1E)-4-oxobut-1-ene-1,2,4-tricarboxylate + H(+) Strongly inhibited by 1 mM Zn(2+), Cu(2+), Mn(2+) and Co(2+) ions. Also inhibited by 5,5'-dithiobis(2-nitrobenzoic acid) (Ellman reagent) in vitro. Optimum pH is 8.4-8.8 for the hydrolysis of 2-pyrone-4,6-dicarboxylate. Induced by 4-hydroxybenzoate. Disruption of this gene results in a strain unable to grow on protocatechuate and a variety of aromatic substrates funnelled through this compound (m- and p-hydroxybenzoate, p-sulfobenzoate, phthalate, isophthalate, terephthalate, vanillate, isovanillate and veratrate). Growth on benzoate and o-aminobenzoate (anthranilate) is not affected in the mutant strain, indicating that these substrates are metabolized via a different lower pathway. Belongs to the metallo-dependent hydrolases superfamily. PDC hydrolase family.