Contributes to the degradation of lignin at the level of the protocatechuate 4,5-cleavage pathway (PubMed:9864312). Catalyzes the hydrolysis of 2-pyrone-4,6-dicarboxylate (PDC) to (4E)-oxalomesaconate (OMA) (PubMed:29658701, PubMed:22475079). The keto form of OMA can tautomerize into the enol form, 4-carboxy-2-hydroxymuconate (CHM), under certain pH conditions (PubMed:22475079). Also catalyzes the reverse reaction (PubMed:22475079, PubMed:9864312). Is essential for the growth of Sphingobium sp. SYK-6 on vanillate but is not responsible for the growth of this strain on syringate (PubMed:9864312). 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+) ions (PubMed:9864312). Also inhibited by pyridine-2,4-dicarboxylic acid, 5-hydroxyisophthalic acid and 5,5'-dithiobis(2-nitrobenzoic acid) (Ellman reagent) (PubMed:22475079, PubMed:9864312). kcat is 342 sec(-1) for the hydrolysis of 2-pyrone-4,6-dicarboxylate (at pH 8.25). kcat is 116 sec(-1) for the synthesis of 2-pyrone-4,6-dicarboxylat from OMA/CHM (at pH 8.25). Optimum pH for hydrolysis of PDC is 8.5 and optimum pH for synthesis of PDC is between 6.0 to 7.5. Optimum temperature is 50 degrees Celsius. Secondary metabolite metabolism; lignin degradation. Monomer. Cells lacking this gene show a complete loss of PDC hydrolase activity and a growth defect on vanillic acid. Growth on syringic acid is not affected. This is the first enzyme from the amidohydrolase superfamily that does not require a divalent metal ion for catalytic activity. Belongs to the metallo-dependent hydrolases superfamily. PDC hydrolase family.