title: Crystal structures of F420-dependent glucose-6-phosphate dehydrogenase FGD1 involved in the activation of the anti-tuberculosis drug candidate PA-824 reveal the basis of coenzyme and substrate binding.
abstract: The modified flavin coenzyme F(420) is found in a restricted number of microorganisms. It is widely distributed in mycobacteria, however, where it is important in energy metabolism, and in Mycobacterium tuberculosis (Mtb) is implicated in redox processes related to non-replicating persistence. In Mtb, the F(420)-dependent glucose-6-phosphate dehydrogenase FGD1 provides reduced F(420) for the in vivo activation of the nitroimidazopyran prodrug PA-824, currently being developed for anti-tuberculosis therapy against both replicating and persistent bacteria. The structure of M. tuberculosis FGD1 has been determined by x-ray crystallography both in its apo state and in complex with F(420) and citrate at resolutions of 1.90 and 1.95 A(,) respectively. The structure reveals a highly specific F(420) binding mode, which is shared with several other F(420)-dependent enzymes. Citrate occupies the substrate binding pocket adjacent to F(420) and is shown to be a competitive inhibitor (IC(50) 43 microm). Modeling of the binding of the glucose 6-phosphate (G6P) substrate identifies a positively charged phosphate binding pocket and shows that G6P, like citrate, packs against the isoalloxazine moiety of F(420) and helps promote a butterfly bend conformation that facilitates F(420) reduction and catalysis.
authors.affiliation: School of Biological Sciences and Centre of Molecular Biodiscovery, University of Auckland, Private Bag 92019, Auckland, New Zealand.
authors.forename: Ghader
authors.initials: G
authors.lastname: Bashiri
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Squire
authors.forename: Nicole J
authors.initials: NJ
authors.lastname: Moreland
authors.forename: Edward N
authors.initials: EN
authors.lastname: Baker
mesh_terms: D000595:Amino Acid Sequence; D000995:Antitubercular Agents / Q000494:pharmacology*; D018360:Crystallography, X-Ray / Q000379:methods; D005954:Glucosephosphate Dehydrogenase / Q000737:chemistry*; D007700:Kinetics; D008956:Models, Chemical; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D020102:Mycobacterium smegmatis / Q000378:metabolism; D009169:Mycobacterium tuberculosis / Q000378:metabolism*; D009593:Nitroimidazoles / Q000737:chemistry / Q000494:pharmacology*; D011485:Protein Binding; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
chemical_list: D000995:Antitubercular Agents; D009593:Nitroimidazoles; C410767:pretomanid; D005954:Glucosephosphate Dehydrogenase