Catalyzes the conversion of 2-hydroxymuconate semialdehyde to 2-hydroxypent-2,4-dienoate. (2Z,4E)-2-hydroxy-6-oxohexa-2,4-dienoate + H2O = 2-oxopent-4-enoate + formate + H(+) Optimum pH is 7-7.5. Aromatic compound metabolism; benzoate degradation via hydroxylation. Belongs to the DmpD/TodF/XylF esterase family.