Highly stable meso-diaminopimelate dehydrogenase from an Ureibacillus thermosphaericus strain A1 isolated from a Japanese compost: purification, characterization and sequencing

We screened various thermophiles for meso-diaminopimelate dehydrogenase (meso-DAPDH, EC 1.4.1.16), which catalyzes the NAD(P)-dependent oxidative deamination of meso-diaminopimelate, and found the enzyme in a thermophilic bacterium isolated from compost in Japan. The bacterium grew well aerobically at around 55 degrees C and was identified as Ureibacillus thermosphaericus strain A1. We purified the enzyme about 47-fold to homogeneity from crude cell extract using five successive purification steps. The molecular mass of the purified protein was about 80 kDa, and the molecule consists of a homodimer with the subunit molecular mass of about 40 kDa. The optimum pH and temperature for the catalytic activity of the enzyme are about 10.5 and 65 degrees C, respectively. The enzyme is highly selective for meso-diaminopimelate as the electron donor, and NADP but not NAD can serve as the electron acceptor. The K-m values for meso-diaminopimelate and NADP at 50 degrees C and pH 10.5 are 1.6 mM and 0.13 mM, respectively. The nucleotide sequence of this meso-DAPDH gene encodes a 326-amino acid peptide. When the gene was cloned and overexpressed in Escherichia coli Rosetta (DE3), the specific activity in the crude extract of the recombinant cells was about 18.0-fold higher than in the extract from U. thermosphaericus strain A1. This made more rapid and simpler purification of the enzyme possible.