The emergence of antibiotic resistance in bacteria that cause life-threatening infections has occurred at an alarming rate in almost every major class of antibiotics. New anti-infective drugs based on novel modes of action are needed. The biosynthesis of isoprenoids is essential because isoprenoids such as steroid hormones, cholesterol and ubiquinone perform vital functions in all living organisms. Several human pathogens, including Mycobacterium tuberculosis and the malaria parasite, Plasmodium falciparum utilize a pathway for isoprenoid biosynthesis that is absent in mammals known as the methylerythritol phosphate (MEP) pathway. Interestingly, despite the diverse structure and function, all isoprenoids originate from two essential bioprecursors, isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP). MEP pathway enzymes synthesize these precursors and are therefore attractive targets for the development of new anti-infective agents. DXP synthase is the first enzyme in the pathway and is a novel class of transketolase-like enzymes. It catalyzes the formation of a C-C bond in the production of deoxy-D-xylulose 5-phosphate from pyruvate and D-glyceraldehyde 3- phosphate. Although DXP synthase possesses some similar characteristics as the mammalian transketolase superfamily, its unique catalytic mechanism and structure point to its potential as a promising anti-infective target. This proposal discusses the results of initial substrate specificity studies which reveal a remarkable affinity of the enzyme for naphthol-based substrates. Our study further highlights catalytic promiscuity of DXP synthase in C-N bond formation. We hypothesize that the naphthol scaffold provides a starting point for the design of selective DXP synthase inhibitors. Initial steps toward inhibitor design are presented in this proposal. In addition, we propose studies that will investigate the mechanism that DXP synthase utilizes in C-N bond formation. The results of these mechanistic studies are expected to highlight unique characteristics of this enzyme which can be exploited in the design of future selective DXP synthase inhibitors.

Public Health Relevance

The work in this proposal has direct impact on infectious diseases such as malaria and tuberculosis. It is focused on learning about chemistry that is unique to DXP synthase, a potentially promising yet insufficiently explored drug target. The long term goal is to develop novel, potent and broad-based anti-microbial agents that also exhibit limited toxicity to the human host.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Predoctoral Individual National Research Service Award (F31)
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Special Emphasis Panel (ZRG1-F04A-G (20))
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Adger-Johnson, Diane S
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Johns Hopkins University
Schools of Medicine
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Bartee, David; Morris, Francine; Al-Khouja, Amer et al. (2015) Hydroxybenzaldoximes Are D-GAP-Competitive Inhibitors of E. coli 1-Deoxy-D-Xylulose-5-Phosphate Synthase. Chembiochem 16:1771-81
Morris, Francine; Vierling, Ryan; Boucher, Lauren et al. (2013) DXP synthase-catalyzed C-N bond formation: nitroso substrate specificity studies guide selective inhibitor design. Chembiochem 14:1309-15