Identification and characterization of 2-keto-3-deoxy-l-rhamnonate dehydrogenase belonging to the MDR superfamily from the thermoacidophilic bacterium Sulfobacillus thermosulfidooxidans: implications to l-rhamnose metabolism in archaea
Suk Min Kim,
Sun Bok Lee
Department of Chemical Engineering, Pohang University of Science and Technology, San 31, Hyoja Dong, Pohang, 790-784, Korea.
We identified the non-phosphorylated l-rhamnose metabolic pathway (Rha_NMP) genes that are homologous to those in the thermoacidophilic archaeon Thermoplasma acidophilum in the genome of the thermoacidophilic bacterium Sulfobacillus thermosulfidooxidans. However, unlike previously known 2-keto-3-deoxy-l-rhamnonate (l-KDR) dehydrogenase (KDRDH) which belongs to the short chain dehydrogenase/reductase superfamily, the putative KDRDHs in S. thermosulfidooxidans (Sulth_3557) and T. acidophilum (Ta0749) belong to the medium chain dehydrogenase/reductase (MDR) superfamily. We demonstrated that Sulth_3559 and Sulth_3557 proteins from S. thermosulfidooxidans function as l-rhamnose dehydrogenase and KDRDH, respectively. Sulth_3557 protein is an NAD+-specific KDRDH with optimal temperature and pH of 50°C and 9.5, respectively. The Km and Vmax values for l-KDR were 2.0 mM and 12.8 U/mg, respectively. Sulth_3557 also showed weak 2,3-butanediol dehydrogenase activity. Phylogenetic analysis suggests that Sulth_3557 and its homologs form a new subfamily in the MDR superfamily. The results shown in this study imply that thermoacidophilic archaea metabolize l-rhamnose to pyruvate and l-lactate by using the MDR-family KDRDH similarly to that of the thermoacidophilic bacterium S. thermosulfidooxidans.
Non-phosphorylated l-rhamnose pathway,
Medium chain dehydrogenase/reductase,