Crystallographic Studies of F 420 ‐dependent Glucose‐6‐phosphate Dehydrogenase from M. tuberculosis

Abstract

F420-dependent Glucose-6-Phosphate Dehydrogenase (FGD) is found within Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB) disease. The fact that the F420 cofactor isn't utilized by humans, makes this enzyme a great candidate for drug development for the treatment of TB. FGD catalyzes the conversion of glucose-6-phosphate (G6P) to 6-phosphogluconolactone (Figure 1). Until our work, these enzymes, in general, have not yet been subjected to rigorous enzymological investigation. Recently, we have unraveled several key pieces of information concerning the hydride transfer mechanism of FGD. However, it is still unclear as to where the substrate, G6P, binds within the active site of FGD, which can be determined through x-ray crystallography using an inactive FGD variant. In 2008, the wild-type FGD crystal structure from Mtb was solved in the presence of citrate, as it was an ingredient in the crystallographic conditions. However, citrate is a competitive inhibitor of the enzyme with respect to G6P. The goal of this project is to solve the crystal structure of FGD in complex with either the natural substrate, G6P, or with a substrate analog that will prevent turnover. For this reason, we propose to synthesize the G6P analog, 1,5-anhydro-D-glucitol-6-phosphate. A concurrent goal has been to optimize crystallographic conditions out of the presence of citrate, using the inactive FGD variant, H40A. Several conditions that exclude citrate have been identified, using screens from Hauptman Woodward Medical Institute, which will be discussed here.