Intradiol ring-cleavage dioxygenases signature

Dioxygenases catalyze the incorporation of both atoms of molecular oxygen into substrates. Cleavage of aromatic rings is one of the most important function of dioxygenases. The substrates of ring-cleavage dioxygenases can be classified into two groups according to the mode of scission of the aromatic ring. Intradiol enzymes cleave the aromatic ring between two hydroxyl groups, whereas extradiol enzymes cleave the aromatic ring between a hydroxylated carbon and another adjacent nonhydroxylated carbon [1]. Intradiol dioxygenases require a nonheme ferric ion as a cofactor. The enzymes that belong to this family are:

• Protocatechuate 3,4-dioxygenase (EC 1.13.11.3) (3,4-PCD), an oligomeric enzyme complex which consists of 12 copies each of an α and a β subunits. Both subunits are evolutionary related.
• Catechol 1,2-dioxygenase (EC 1.13.11.1) (gene catA or clcA).
• Chlorocatechol 1,2-dioxygenase (EC 1.13.11.1) (gene tfdC).

As a signature pattern for these enzymes we selected a region that includes a tyrosine residue which, in 3,4-PCD, has been shown [2], to be implicated in the binding of the ferric iron atom.