UCLA

Rising to dangerously high levels all over the world, antibiotic resistance is now a critical global problem. To inhibit or kill bacteria, most antibiotics target the growth process of bacterial cells. Therefore, most antibiotics are ineffective for slowly growing bacteria with lower cellular influx. Current therapeutic approaches most commonly utilize broad-spectrum antibiotics and/or drug cocktails to target a wide range of bacteria. Unfortunately, broad-spectrum antibiotics can target both beneficial and pathogenic bacteria. This nonspecificity imparts significant pressure on bacterial species to evolve into resistant strains. In addition, beneficial bacteria do not always fully recover, increasing susceptibility to infections and diseases. It is not practical to develop antibiotics for all species of interest. To mitigate these issues, we must engineer new antibiotics in a drastically different way to prevent running out of effective therapies. Bacteria are capable of producing defensive molecules. These secreted multi-functional molecules inhibit other closely related strains competing for the same environmental niches. We were inspired by the defensive behavior of bacteria to engineer novel antibiotics featuring tunable functionalityThis tunability allows for an adjustable bandwidth of antimicrobial activity against multiple species within a specific set of environmental conditions. Moreover, we produced antibiotics able to inhibit pathogenic bacteria without harming host cells or beneficial commensal bacteria. We were interested in antimicrobial peptides (AMPs) as antibiotics, since they target generic features common to the outer membrane of many pathogenic species. These antibiotics allow us to regulate complex microbial communities by inhibiting or killing detrimental bacteria without harming host-associated microbial communities, that have beneficial impacts on human health. Additionally, these new antibiotics help beneficial bacteria win the competition over environmental niches. Therefore, the development of resistance is significantly inhibited compared to that of conventional antibiotics. To engineer new antimicrobials, we leveraged recently developed sequence design rules, using both positive charge and hydrophobicity as necessary conditions for antimicrobial activity. These hybrid antimicrobial molecules can be used for treating resistant infections and regulating species distribution in microbial communities. We engineered tunable antimicrobial peptides with a ‘threshold’ activity profile using pH-switchable charge. To tune the antimicrobial activity of α−helical AMPs, we modified functional groups on the side chain of specific basic amino acids (lysine and arginine). By incorporating electron withdrawing and/or hydrophobic compounds on the side chains of arginine and lysine residues, the pKa at which these residues become positively charged can be lowered. Therefore, by incorporating different masking groups in different locations, we adjust the activity of the antimicrobial peptides by turning them on at specific and tunable pH values.