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

Abstract 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 with NAD+/NADP+ as a cofactor. The purified enzyme 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, the purified TmAraDH had highest specific activity towards L-arabinose, D-galactose and D-fucose. The catalytic efficiency (kcat/Km) towards L-arabinose and D-galactose was 123.85, 179.26 min− 1mM− 1 for NAD+, and 56.06, 18.19 min− 1mM− 1 for NADP+, respectively, and those for NAD+ and NADP+ were 374.64 and 2001.64 min− 1mM− 1 using D-galactose, and 227.98 and 2661.27 min− 1mM− 1 using L-arabinose, respectively. TmAraDH exhibited complete conversion in 12 h at 70oC 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 into rare sugar acids.