3dioxygenase

3dioxygenase refers to a class of enzymes that incorporate two atoms of oxygen into a substrate molecule, typically at a third carbon position (C-3). These enzymes are monooxygenase-like oxidases that perform stereo‑selective oxidations. They are often classified under the EC 1.14 category of oxidoreductases that use oxygen as an acceptor.

Many 3dioxygenases belong to the α‑ketoglutarate (αKG)‑dependent dioxygenase family. They require Fe(II) as a cofactor and αKG as a co‑substrate. In these enzymes, O₂ is split: one oxygen atom is incorporated into the substrate, while the other is oxidized to CO₂ and succinate derived from αKG. Structure–function studies show an iron‐binding motif (HXD/E…H) arranged on the N‑terminal domain, with a conserved HPX…H motif that coordinates the Fe(II). The active site adopts a characteristic fold that stabilizes the transition state and directs oxygen delivery to the C‑3 atom of the substrate.

A well‑studied member is the human 3‑hydroxyanthranilate 3,4‑dioxygenase (H3HAA), a key enzyme in the kynurenine pathway of tryptophan degradation. H3HAA catalyzes the opening of the benzoquinone ring at C‑3, producing 2‑aminomuconate‑6‑semialdehyde. Deficiencies in this enzyme lead to accumulation of 3‑hydroxyanthranilate, which has been implicated in neurodegenerative diseases such as Huntington’s disease and multiple sclerosis. Several bacterial 3dioxygenases participate in the biosynthesis of secondary metabolites, including pigments and antibiotics.

Catalytic mechanisms generally involve the chelation of Fe(II), decarboxylation of αKG, and formation of a highly reactive Fe(IV)=O species that abstracts a hydrogen atom from the substrate at the C‑3 position. The resulting radical recombines with the hydroxyl fragment, producing the oxidized product while releasing reduced αKG products.

Because of their role in essential metabolic pathways and secondary metabolite production, 3dioxygenases have attracted biotechnological interest. Engineered variants can be employed in biocatalysis to produce enantiopure hydroxy compounds with applications in pharmaceuticals and fine chemicals.