Systematic mutagenesis of oncocin reveals enhanced activity and insights into the mechanisms of antimicrobial activity*

Oncocin is a proline-rich antimicrobial peptide that inhibits protein synthesis by binding to the bacterial ribosome. The aim of this work is to improve the antimicrobial activity of oncocin by systematic peptide mutagenesis and activity evaluation. We discovered that a pair of cationic substitutions (P4K and P7K/R) enhanced the activity by 2 to 4 fold (p<0.05) against multiple Gram-negative bacteria. An in vitro transcription / translation assay indicated that the increased activity was not because of stronger ribosome binding. Instead a cellular internalization assay revealed a higher internalization rate for the optimized analogs thereby suggesting a mechanism to increase potency. In addition, we found that the optimized peptides' benefit is dependent upon nutrient-depleted media conditions.