Antimicrobial Peptide Activity in E. coli at Multiple Scales

(supported by the Austrian Science Fund, Project No. P 30921)

start of project: 01. 01. 2018
end of project: 30. 06. 2021

Multi-resistant pathogenic bacteria rapidly gain grounds world-wide, especially in health-care units, representing a global health problem with a strong social and economic impact. Hence, the World Health Organization emphasized the urgent need for the development of antibiotics with novel mechanisms of action to counteract the steady decline of approved antibiotics since the early 1980s. One highly promising and alternative strategy to conventional antibiotics is based on antimicrobial peptides (AMPs), effector molecules of the innate immune system that provide a first line of defense against invaders. The peculiarity of AMPs in comparison to conventional antibiotics is that they interfere physically with the barrier function of the cell envelope of bacteria and do not interact with specific target molecules. Furthermore, owing to their killing of bacteria within minutes, evolvement of resistance is less likely.

However despite the insight on molecular interactions gained from studies on model systems, there is no comprehensive picture of how AMPs affect bacterial cells and actually kill bacteria. In particular, the kinetic and spatial evolution of processes at the different structural levels of the cell envelope (e.g. cell wall and cell membrane) is currently unknown. In order to fully understand their mechanism of action it is essential to bridge this gap. To address this issue we suggest performing time-resolved X-ray scattering experiments on live Escherichia coli and monitor their response to AMPs. This highly innovative approach will enable us for the first time to probe changes at the molecular and microscopic level in real time. Preliminary experiments at the synchrotron in Grenoble demonstrated for the first time that structural changes induced by AMPs occur on the sub-second time scale, which is much faster than anticipated. Our studies will initially focus on AMPs derived from human lactoferrin, a protein enriched in breast milk, developed within a European project coordinated by the main applicant. The primary target of these peptides is known to be the bacterial cell envelope.

The aim of the proposal is to dissect structural changes in bacteria especially cell envelope upon AMP attacks and to follow their progression as killing proceeds. The gained insight will be transferred to future studies on other AMPs and other clinically relevant bacteria such as Staphylococcus aureus, paving the way towards a comprehensive understanding of the molecular killing mechanism of AMPs. This knowledge will facilitate their development into novel and effective compounds for therapeutic applications in infectious diseases caused by antibiotic-resistant pathogens.