Characterization of dye-linked d-amino acid dehydrogenase from Sulfurisphaera tokodaii expressed using an archaeal recombinant protein expression system.

A gene encoding a dye-linked d-amino acid dehydrogenase (Dye-DADH) homologue was found in a hyperthermophilic archaeon, Sulfurisphaera tokodaii. The predicted amino acid sequence suggested that the gene product is a membrane-bound type enzyme. The gene was overexpressed in Escherichia coli, but the recombinant protein was exclusively produced as an inclusion body. In order to avoid production of the inclusion body, an expression system using the thermoacidophilic archaeon Sulfolobus acidocaldarius instead of E. coli as the host cell was constructed. The gene was successfully expressed in Sulfolobus acidocaldarius, and its product was purified to homogeneity and characterized. The purified enzyme catalyzed the dehydrogenation of various d-amino acids, with d-phenylalanine being the most preferred substrate. The enzyme retained its full activity after incubation at 90 °C for 30 min and after incubation at pH 4.0-11.0 for 30 min at 50 °C. This is the first report on membrane-bound Dye-DADH from thermophilic archaea that was successfully expressed in an archaeal host.