Functional and regulatory interdependence of small proteins during membrane depolarization and persister cell formation in Escherichia coli
Giessen University, Institute for Microbiology and Molecular Biology
There is increasing evidence that several small hydrophobic proteins (mainly toxins from type I toxin-antitoxin systems) target the inner membrane, leading to depolarization and ATP depletion. ATP depletion is an important trigger for growth retardation and subsequent persister cell formation. Persisters are multidrug-tolerant cells with a high clinical relevance due to their ability to survive antibiotic treatments. The project aims to increase our knowledge of depolarized cells with regard to cell physiology and the underlying interactions of toxins. We will study the type I toxin-antitoxin system TisB/IstR-1 from E. coli as a model system. The small toxin TisB (29 amino acids) is known to cause depolarization and to trigger persistence under DNA damage conditions. According to the “charge zipper” model, TisB dimers localize to the inner membrane and form salt bridges along which protons can pass across the membrane. The TisB “charge zipper” model will be tested in vivo with regard to toxin functionality. Furthermore, it will be investigated how depolarization affects downstream stress responses and cross-activation of other toxins through depletion of ATP or generation of reactive oxygen species. It will also be addressed whether TisB interacts with other (small) proteins or protein complexes in the inner membrane. Finally, results from E. coli will be compared to distantly related bacteria and archaea to appreciate the universality of membrane depolarization by small proteins as strategy for persister generation and survival.
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