A small-molecule inhibitor of BamA impervious to efflux and the outer membrane permeability barrier

Elizabeth M. Hart, Angela M. Mitchell, Anna Konovalova, Marcin Grabowicz, Jessica Sheng, Xiaoqing Han, Frances P. Rodriguez-Rivera, Adam G. Schwaid, Juliana C. Malinverni, Carl J. Balibar, Smaranda Bodea, Qian Si, Hao Wang, Michelle F. Homsher, Ronald E. Painter, Anthony K. Ogawa, Holly Sutterlin, Terry Roemer, Todd A. Black, Deborah M. RothmanScott S. Walker, Thomas J. Silhavy

Research output: Contribution to journalArticlepeer-review

113 Scopus citations


The development of new antimicrobial drugs is a priority to combat the increasing spread of multidrug-resistant bacteria. This development is especially problematic in gram-negative bacteria due to the outer membrane (OM) permeability barrier and multidrug efflux pumps. Therefore, we screened for compounds that target essential, nonredundant, surface-exposed processes in gram-negative bacteria. We identified a compound, MRL-494, that inhibits assembly of OM proteins (OMPs) by the β-barrel assembly machine (BAM complex). The BAM complex contains one essential surface-exposed protein, BamA. We constructed a bamA mutagenesis library, screened for resistance to MRL-494, and identified the mutation bamAE470K. BamAE470K restores OMP biogenesis in the presence of MRL-494. The mutant protein has both altered conformation and activity, suggesting it could either inhibit MRL-494 binding or allow BamA to function in the presence of MRL-494. By cellular thermal shift assay (CETSA), we determined that MRL-494 stabilizes BamA and BamAE470K from thermally induced aggregation, indicating direct or proximal binding to both BamA and BamAE470K. Thus, it is the altered activity of BamAE470K responsible for resistance to MRL-494. Strikingly, MRL-494 possesses a second mechanism of action that kills gram-positive organisms. In microbes lacking an OM, MRL-494 lethally disrupts the cytoplasmic membrane. We suggest that the compound cannot disrupt the cytoplasmic membrane of gram-negative bacteria because it cannot penetrate the OM. Instead, MRL-494 inhibits OMP biogenesis from outside the OM by targeting BamA. The identification of a small molecule that inhibits OMP biogenesis at the cell surface represents a distinct class of antibacterial agents.

Original languageEnglish (US)
Pages (from-to)21748-21757
Number of pages10
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number43
StatePublished - Oct 22 2019

All Science Journal Classification (ASJC) codes

  • General


  • Antibiotic development
  • BAM complex
  • Escherichia coli
  • Gram-negative bacteria
  • Outer membrane biogenesis


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