Identification of an extremely thermostable enzyme with dual sugar-1-phosphate nucleotidylyltransferase activities from an acidothermophilic archaeon, Sulfolobus tokodaii strain 7

L-Rhamnose is an essential component of the cell wall and plays roles in mediating virulence and adhesion to host tissues in many microorganisms. Glucose-1-phosphate thymidylyltransferase ( RmlA, EC 2.7.7.24) catalyzes the first reaction of the four-step pathway of L-rhamnose biosynthesis, producing dTDP-D-glucose from dTTP and glucose-1-phosphate. Three RmlA homologues of varying size have been identified in the genome of a thermophilic archaeon, Sulfolobus tokodaii strain 7. In this study, we report the heterologous expression of the largest homologue (a 401 residue-long ST0452 protein) and characterization of its thermostable activity. RmlA enzymatic activity of this protein was detected from 65 to 100 degreesC, with a half- life of 60 min at 95 degreesC and 180 min at 80 degreesC. Analysis of a deletion mutant lacking the 170-residue C-terminal domain indicated that this region has an important role in the thermostability and activity of the protein. Analyses of substrate specificity indicated that the enzymatic activity of the full- length protein is capable of utilizing alpha-D-glucose-1-phosphate and N-acetyl-D-glucosamine-1-phosphate but not alpha-D glucosamine1- phosphate. However, the protein is capable of utilizing all four deoxyribonucleoside triphosphates and UTP. Thus, the ST0452 protein is an enzyme containing both glucose- 1-phosphate thymidylyltransferase and N-acetyl-D-glucosamine-1-phosphate uridylyltransferase activities. This is the first report of a thermostable enzyme with dual sugar-1-phosphate nucleotidylyltransferase activities.