UNDERSTANDING THE ANTIMICROBIAL ACTIVITY OF THE EARLY STAGE MEP PATHWAY INHIBITORS
Embargo until
2022-12-01
Date
2018-06-07
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Johns Hopkins University
Abstract
Toward combating the growing problem of antibiotic resistance, this work describes the investigation of the E. coli enzyme, DXP synthase, as a novel drug target. DXP synthase is a branchpoint enzyme involved in thiamin diphosphate, pyridoxal phosphate, and isoprenoid biosynthesis in bacteria. Previous work uncovered the unique catalytic mechanism of DXP synthase and correspondingly large active site volume. These features have guided the design of sterically demanding alkylacetylphosphonates (alkylAPs) toward the development of selective DXP synthase inhibitors. AlkylAPs display selective, low μM inhibitory activity against DXP synthase. They are weak inhibitors of bacterial growth in standard nutrient rich conditions. However, bacteria are significantly sensitized to most alkylAPs in defined minimal growth medium, with minimal inhibitory concentrations ranging from low μM to low mM and influenced by alkyl-chain length. DXP synthase expression and thiamin supplementation studies offer support for DXP synthase as an intracellular target for some alkylAPs and reveal the challenges of these approaches to study target engagement.
Despite weak growth inhibition in rich medium, butylacetylphosphonate (BAP) was found to act synergistically with fosmidomycin (FOS), an inhibitor of the first committed step in the isoprenoid biosynthesis pathway, under these conditions. Like BAP, FOS antibacterial activity is medium-dependent. However, in contrast to BAP, FOS is more potent in rich than minimal medium. Finally, the relationship between BAP and FOS in combination is growth medium-dependent; BAP and FOS are synergistic in rich medium but indifferent in minimal medium. The loss of BAP-FOS synergy in minimal medium implies a shift in the metabolic network surrounding DXP synthase, which may have important implications in treatment of bacterial infections. The dependence of inhibitor potency on growth environment emphasizes the need for antimicrobial screening conditions that are relevant to the in vivo microbial microenvironment during infection.
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Keywords
bacterial metabolism, DXP synthase