- 3-Hydroxyanthranilate 3,4-dioxygenase (HAO) is an iron-dependent protein that activates O2 and inserts both oxygen atoms into 3-hydroxyanthranilate (3-HAA). An intriguing question is how HAO can rapidly bind O2, even though local O2 concentrations and diffusion rates are relatively low. Here, a close inspection of the HAO structures revealed that substrate- and inhibitor-bound structures exhibit a closed conformation with three hydrophobic loop regions moving toward the catalytic iron center, whereas the ligand-free structure is open.
- The kynurenine pathway is the primary route for l-tryptophan degradation in mammals. Intermediates and side products of this pathway are involved in immune response and neurodegenerative diseases. This makes the study of enzymes, especially those from mammalian sources, of the kynurenine pathway worthwhile. Recent studies on a bacterial version of an enzyme of this pathway, 2-aminomuconate semialdehyde (2-AMS) dehydrogenase (AMSDH), have provided a detailed understanding of the catalytic mechanism and identified residues conserved for muconate semialdehyde recognition and activation.
- Aldehyde dehydrogenase typically performs oxidation of aldehydes to their corresponding carboxylic acid while reducing NAD(P)+ to NAD(P)H via covalent catalysis mediated by an active-site cysteine residue. One member of this superfamily, the enzyme 2-aminomuconate-6-semialdehyde dehydrogenase (AMSDH), is a component of the kynurenine pathway, which catabolizes tryptophan in mammals and certain bacteria. AMSDH catalyzes the NAD+-dependent oxidation of 2-aminomuconate semialdehyde to 2-aminomuconate.