Molecular characterization of PadA, a phenylacetaldehyde dehydrogenase from Escherichia coli

The padA gene encoding the phenylacetaldehyde dehydrogenase involved in the catabolism of 2-phenylethylamine in Escherichia coli has been cloned, sequenced, and located at 31.0 min on the chromosome. The deduced PadA polypeptide contains 499 amino acid residues with a predicted molecular mass of 53.7 kDa, and its primary structure reveals significant similarity with that of members of the aldehyde dehydrogenase superfamily. By engineering optimal transcription and translation elements, a high expression of the padA gene has been achieved. The active PadA enzyme is a homodimer that prefers NAD+ over NADP+ as coenzyme. The enzyme efficiently oxidizes only phenylacetaldehyde-like aromatic aldehydes, and has a weak esterase activity with p-nitrophenol. The padA gene constitutes a new catabolic tool for designing DNA cassettes to expand the abilities of microorganisms to degrade toxic aromatic compounds.