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 °C and pH 8.0, and retained 63.7% of its activity after 24 h at 60 °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 (kcat/Km) 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 °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.