EAGER: Mechanism of toxin activation and function in bacteria

All biological organisms are exposed to environmental stress conditions, which lead to physiological responses at the cellular level. In bacteria, environmental stress can cause the production of proteins that alter metabolism, the production and maintenance of cellular components, growth, and survivability. A class of proteins comprising this physiological response to stress in bacteria includes toxin-antitoxin (TA) systems.

These TA systems are produced, activated, and inactivated in the bacterial cell to control the toxin activity and modify the cellular response to stress. TA systems have also been implicated in biofilm formation, colonization, virulence, and antibiotic tolerance with implications in environment and health. However, our understanding of how TA systems are regulated is limited.

Overcoming this barrier would allow for the development of new strategies to control TA system activity, thereby targeting the TA-related functions, such as tolerance to antibiotics or biofilm development. This work will utilize an integrated genetic, structural, biochemical and biophysical approach to study these important biological regulatory systems.

A second outcome of this work will be a detailed understanding of how proteins, including degradative enzymes, destroy TA system components. More broadly, this project will support the training of students in this advanced, multidisciplinary field, and prepare them for a future career at the forefront of science, technology, engineering and mathematics (STEM).

The model TA system of MqsRA includes the ribonuclease toxin, MqsR, and its cognate antitoxin, MqsA. MqsR activation leads to cleavage of messenger RNAs at specific sequence sites. Acting as a regulatory switch, TA system activity is elicited by proteolysis of the inhibitory antitoxin, thus altering the antitoxin-toxin ratio and allowing the free toxin to become active.

These studies will elucidate the recognition determinants for degradation of MqsA by two cellular proteases that enable MqsR activation. Further, this work will determine the mechanism of protease-regulated activation of toxin in live cells and evaluate roles of key stress-induced chaperones in modifying MqsA susceptibility. This approach will incorporate multidisciplinary strategies and techniques to discover the biochemical, molecular, and cellular determinants for TA system regulation to inform survival strategies in bacteria.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.