The Active Component of Dehydrophos Covalently Binds to Acetohydroxyacid Synthase and Inhibits the Growth of Uropathogenic Escherichia coli

Acetohydroxyacid synthase (AHAS) is the first enzyme in the branched-chain amino acid biosynthesis pathway and is the target for more than 50 commercially deployed herbicides. This enzyme has also been suggested as a target for the discovery of novel antimicrobial and antifungal therapeutics. Dehydrophos, a natural product antibiotic, is a potential new lead inhibitor of AHASs for drug development, whereby the biologically active component is proposed to be methyl acetylphosphonate (MAP). MAP has been suggested as a pyruvate analog that inhibits ThDP-dependent enzymes, including AHAS. Here, the crystal structure of Saccharomyces cerevisiae AHAS in complex with MAP has been determined to 2.22 Å resolution, showing that it binds covalently with ThDP. We have also shown that MAP alone is effective in inhibiting the growth of uropathogenic Escherichia coli (UPEC) in cell susceptibility assays and that this activity is lost when exogenous branched-chain amino acids (BCAAs) are added. This suggests that AHAS is a target for the antibiotic activity of MAP and dehydrophos. Our crystal structure provides a starting point for the rational design of ThDP covalently bound AHAS inhibitors that are also structurally different from those that have been developed previously as commercial herbicides that inhibit AHAS.