Structural and Functional Studies of GDP-6-Deoxy-Talose and GDP-Rhamnose Biosynthetic Enzymes

GDP-6-deoxy-D-talose and its 4-epimer GDP-D-rhamnose are unusual sugars found on the cell surface of certain Gram-negative bacteria. GDP-6-deoxy-talose and GDP-rhamnose are produced by enzymes called GTS and RMD, respectively. These sugars are produced from the same common intermediate and are 4\u27-epimers of each other, which provides an interesting paradigm to study the stereo-selective reduction of unusual sugars. We have determined a novel X-ray crystallographic structure of RMD from Pseudomonas aeruginosa that contains its cosubstrate NADPH within the active site. A superposition of our RMD structure with a previously-determined one gives clear insight into the mechanism of hydride transfer from the cofactor during catalysis. We also report progress toward the structural analysis of GTS and functional analyses of both enzymes. Characterization of GTS and RMD will allow for an understanding of how bacteria utilize these sugars and may give insight into the pathogenicity of certain Gram-negative bacteria. Furthermore, an understanding of the production of unusual sugars can allow for the derivitization of existing antibiotics in an effort to combat bacterial resistance via a process called glycodiversification