Characterization of NADP+-specific L-rhamnose dehydrogenase from the thermoacidophilic Archaeon Thermoplasma acidophilum

utilizes -rhamnose as a sole carbon source. To determine the metabolic pathway of -rhamnose in Archaea, we identified and characterized -rhamnose dehydrogenase (RhaD) in . Ta0747P gene, which encodes the putative RhaD (Ta_RhaD) enzyme belonging to the short-chain dehydrogenase/reductase family, was expressed in as an active enzyme catalyzing the oxidation of -rhamnose to -rhamnono-1,4-lactone. Analysis of catalytic properties revealed that Ta_RhaD oxidized -rhamnose, -lyxose, and -mannose using only NADP(+) as a cofactor, which is different from NAD(+)/NADP(+)-specific bacterial RhaDs and NAD(+)-specific eukaryal RhaDs. Ta_RhaD showed the highest activity toward -rhamnose at 60 A degrees C and pH 7. The (m) and (cat) values were 0.46 mM, 1,341.3 min(-1) for -rhamnose and 0.1 mM, 1,027.2 min(-1) for NADP(+), respectively. Phylogenetic analysis indicated that branched lineages of archaeal RhaD are quite distinct from those of Bacteria and Eukarya. This is the first report on the identification and characterization of NADP(+)-specific RhaD.