Characterization of a thermostable 2,4-diaminopentanoate dehydrogenase from Fervidobacterium nodosum Rt17-B1

• This is the first report of a thermostable 2,4-diaminopentanoate dehydrogenase.
• The enzyme acts not only on 2,4-diaminopentanoate but also on 2,5-diaminohexanoate.
• The enzyme is expected to be useful for the production of chiral amine compounds.
• Uncompetitive inhibition by 2,4-diaminopentanoate and d-ornithine was discovered.
• A regulatory role for this enzyme in oxidative ornithine degradation is suggested.

2,4-Diaminopentanoate dehydrogenase (2,4-DAPDH), which is involved in the oxidative ornithine degradation pathway, catalyzes the NAD+- or NADP+-dependent oxidative deamination of (2R,4S)-2,4-diaminopentanoate (2,4-DAP) to form 2-amino-4-oxopentanoate. A Fervidobacterium nodosum Rt17-B1 gene, Fnod_1646, which codes for a protein with sequence similarity to 2,4-DAPDH discovered in metagenomic DNA, was cloned and overexpressed in Escherichia coli, and the gene product was purified and characterized. The purified protein catalyzed the reduction of NAD+ and NADP+ in the presence of 2,4-DAP, indicating that the protein is a 2,4-DAPDH. The optimal pH and temperature were 9.5 and 85°C, respectively, and the half-denaturation time at 90°C was 38 min. Therefore, the 2,4-DAPDH from F. nodosum Rt17-B1 is an NAD(P)+-dependent thermophilic-alkaline amino acid dehydrogenase. This is the first thermophilic 2,4-DAPDH reported, and it is expected to be useful for structural and functional analyses of 2,4-DAPDH and for the enzymatic production of chiral amine compounds. Activity of 2,4-DAPDH from F. nodosum Rt17-B1 was suppressed by 2,4-DAP via uncompetitive substrate inhibition. In contrast, the enzyme showed typical Michaelis–Menten kinetics toward 2,5-diaminohexanoate. The enzyme was uncompetitively inhibited by d-ornithine with an apparent Ki value of 0.1 mM. These results suggest a regulatory role for this enzyme in the oxidative ornithine degradation pathway.