Properties of the L-Galactose Dehydrogenase from Pseudoalteromonas atlantica T6c

Abstract

In a previous study from our laboratory, L-galactose in red seaweeds has been utilized as a substrate for bioethanol production by metabolically engineered E. coli KO11. L-Galactose dehydrogenase (LGDH) from Pseudoalteromonas atlantica T6c (Patl_LGDH) is one of the three enzymes that were introduced into the recombinant E. coli. In this study, we characterized the enzymatic properties of Patl_LGDH which belongs to the AKR superfamily (COG 0667) and compared its properties with other LGDHs. The amino acid sequence of the Patl_LGDH showed identities of 47%, 44%, 45% and 47% with LGDHs from Arabidopsis thaliana, Spinacia oleracea, Prunus persica and Bacteroides vulgatus, respectively. Multiple sequence alignment indicated that the catalytic tetrad of the AKR family is conserved in Patl_LGDH. Optimal temperature and pH of Patl_LGDH were 30°C and pH 8.0, respectively. The highest activity was shown for L-galactose with Km value of 1.81×10-3 M, kcat value of 76.6 s-1 and kcat/Km value of 4.24×104 s-1M-1. It was found that Patl_LGDH uses only NADP+ as a cofactor with very low activity toward L-gulose (1.4%) and L-glucose (0.8%). When NAD+ was used as a cofactor, Patl_LGDH showed no activity toward the sugars tested in this study.