Elucidating the membrane properties regulating antimicrobial peptidebinding to bacterial vesicles

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Project Summary Antimicrobial peptides (AMPs), such as LL-37, have been proposed as potential next-generation antibiotics due to their ability to bind to and disrupt the bacterial cell membrane. However, their use has been limited by several factors, including inactivation by binding to bacterial outer membrane vesicles (OMVs). OMVs are derived from the outer membrane (OM) of Gram-negative bacteria and therefore have a similar membrane composition as the OM. OMVs are heterogeneous in their physical and chemical properties, including size, charge, and lipid and protein composition, even among OMVs produced by the same parent bacterium. Traditional methods to study protein/peptide interactions with OMVs use bulk measurements, which result in ensemble averages that can obscure the influence OMV heterogeneity has on these interactions. We have developed several approaches that enable us to study protein-lipid interactions in OMVs on single-vesicle and subpopulation levels, which we will use in this project to uncover the specific properties that regulate LL-37 binding to OMVs. We will first use liposomes with controlled compositions to identify the roles of vesicle size, charge, lipid saturation, and LPS composition in LL-37 binding. Next, we will use OMVs with varying sizes and charges to relate LL-37 affinity to the OMVs’ ability to protect bacterial cells from the activity of LL-37. Finally, we will investigate how the properties of OMVs change upon exposure of the bacteria to LL-37 and how these changes affect LL-37 binding to OMVs. Undergraduate and graduate students will be highly involved in all of the proposed studies, and the Investigators are committed to mentoring these students to maximize their development of technical, critical thinking, and communication skills. We anticipate that the results generated from this project will inform the future design of more effective AMPs.