Gene cloning and characterization of a deaminase from the 4-amino-3-hydroxybenzoate-assimilating Bordetella sp. strain 10d

The 4-amino-3-hydroxybenzoate-assimilating Bordetella sp. strain 10d produces a deaminase that catalyzes the deamination of 2-amino-5-carboxymuconic 6-semialdehyde. A gene encoding the deaminase, ahdB , was cloned and expressed in Escherichia coli; ahdB is located downstream from the previously reported genes encoding 4-amino-3-hydroxybenzoate 2,3-dioxygenase ( ahdA ) and a LysR-type regulator. The deduced amino acid sequence of ahdB shows 30–33% identity to those of previously reported 2-aminomuconate deaminases. We identified a region (RAGDFLXVSG) conserved in AhdB and three other deaminases. The recombinant enzyme AhdB was purified to homogeneity. After a coupled enzyme assay with purified AhdA, AhdB, and the substrate 4-amino-3-hydroxybenzoate, the final product, formed by the action of AhdA, AhdB, and by nonenzymatic decarboxylation, was identified by HPLC, MS, and ¹H-nuclear magnetic resonance analyses as 2-hydroxymuconic 6-semialdehyde.