UDP-N-Acetylmuramic Acid l-Alanine Ligase (MurC) Inhibition in atolCMutant Escherichia coli Strain Leads to Cell Death
ABSTRACTThe Mur ligases play an essential role in the biosynthesis of bacterial peptidoglycan and hence are attractive antibacterial targets. A screen of the AstraZeneca compound library led to the identification of compound A, a pyrazolopyrimidine, as a potent inhibitor ofEscherichia coliandPseudomonas aeruginosaMurC. However, cellular activity againstE. coliorP. aeruginosawas not observed. Compound A was active against efflux pump mutants of both strains. Experiments using anE. colitolCmutant revealed accumulation of the MurC substrate and a decrease in the level of product upon treatment with compound A,indicating inhibition of MurC enzyme in these cells. Such a modulation was not observed in theE. coliwild-type cells. Further, overexpression of MurC in theE. colitolCmutant led to an increase in the compound A MIC by ≥16-fold, establishing a correlation between MurC inhibition and cellular activity. In addition, estimation of the intracellular compound A level showed an accumulation of the compound over time in thetolCmutant strain. A significant compound A level was not detected in the wild-typeE. colistrain even upon treatment with high concentrations of the compound. Therefore, the lack of MIC and absence of MurC inhibition in wild-typeE. coliwere possibly due to suboptimal compound concentration as a consequence of a high efflux level and/or poor permeativity of compound A.