Developing Peptide Probes for Membrane Lipids via Phage Display

Abstract

Lipid reporters are key signaling molecules in a number of biological processes ranging from apoptosis in mammalian cells to novel resistance mechanisms in pathogenic bacteria. Developing probes to target these lipids is a worthy endeavor, especially when better reporters could mean lives saved. This is particularly true considering new antibiotic resistant pathogens emerge every year with evolving lipid compositions. To combat these pathogens and prevent a potential global pandemic, it is imperative to continue the development of novel and innovative probes/drugs to meet this daunting challenge. To fulfill this demand, we must continue to establish new strategies, enhance current technologies and advance scientific understanding. Only by pushing the boundaries of what is currently possible will we remain one step ahead of these diseases. Diseases like mcr-1 positive bacteria, first documented in 2016, remain largely uncontested. Herein, we seek to expand the available probes specific to key lipid reporters for phosphatidylserine, lysyl-phosphatidylglycerol, and phosphoethanolamine lipid A. Cyclic phage libraries were first utilized to target phosphatidylserine, ultimately producing weak binders. Refining our phage display libraries to include reversible covalent warheads allowed for the identification of more potent lipid reporters. In doing so, we have created the tools necessary to interrogate the unique resistance mechanisms expressed by these drug-resistant pathogens. A strong correlation was observed between peptides binding mcr-1 positive strains, LPS modification on the surface of these bacteria, and level of colistin resistance. To our knowledge, these peptides are the only probes capable of demonstrating this correlation. We surmise that the methods discussed here will pave the way for better diagnostic tools for these resistant pathogens. A recurring method of resistance among gram-positive and gram-negative bacteria has been to decorate their surface with positive amines to repel cationic antimicrobial peptides. As such, our current APBA library and the libraries in development in the Gao lab would be ideally suited to target these and other undiscovered resistance mechanisms.