Characterization of L-arabinose/D-galactose 1-dehydrogenase from Thermotoga maritima and its application in galactonate production

The first hyperthermophilic L-arabinose/D-galactose 1-dehydrogenase (TmAraDH) from Thermotoga maritima was heterologously purified from Escherichia coli. It belongs to the Gfo/Idh/MocA protein family, prefers NAD(+)/NADP(+) as a cofactor. The purified TmAraDH exhibited maximum activity toward L-arabinose at 75 degrees C and pH 8.0, and retained 63.7% of its activity after 24 h at 60 degrees C, and over 60% of its activity after holding a pH ranging from 7.0 to 9.0 for 1 h. Among all tested substrates, TmAraDH exclusively catalyzed the NAD(P)(+)-dependent oxidation of L-arabinose, D-galactose and D-fucose. The catalytic efficiency (k(cat)/K-m) towards L-arabinose and D-galactose was 123.85, 179.26 min(-1) mM(-1) for NAD(+), and 56.06, 18.19 min(-1) mM(-1) for NADP(+), respectively. TmAraDH exhibited complete oxidative conversion in 12 h at 70 degrees C to D-galactonate with 5 mM D-galactose. Modelling provides structural insights into the cofactor and substrate recognition specificity. Our results suggest that TmAraDH have great potential for the conversion of L-arabinose and D-galactose to L-arabonate and D-galactonate.