Proposed Mechanisms of Tethered Antimicrobial Peptide Chrysophsin-1 as a Function of Tether Length Using QCM-D

Rising antibiotic resistance has led to a call for the development of alternative antibiotics. Antimicrobial peptides (AMPs) are promising, but their potential has not been fully explored because of toxicity and lack of stability in vivo. Multiple recent studies have focused on surface immobilization of AMPs to maximize antimicrobial activity and stability while mitigating toxicity. We covalently tethered cysteine-modified chrysophsin-1 (C-CHY1) via PEG of three molecular weights, 866, 2000, and 7500. Quartz crystal microbalance with dissipation (QCM-D) was used to characterize thickness and grafting density of tethered C-CHY1, which were related to its activity against Staphylococcus aureus and Escherichia coli and found to be important in determining mechanisms leading to activity. The PEG 866 tether promoted an antimicrobial mechanism that caused displacement of positive cations from bacterial membranes. The PEG 7500 tether maintained C-CHY1's ability to effectively form membrane pores, promoting the highest activity. When AMP was tethered with PEG 2000, antimicrobial activity was limited, apparently because neither mechanism of AMP activity was able to occur with this tether. Using QCM-D, we calculated thickness and density of PEG-tethered C-CHY1 and correlated it with antimicrobial effectiveness to determine the mechanisms by which tethered C-CHY1 acts against bacteria.