Point Mutation In The Hydrophobic Region Drives Selectivity And Activity Of Op-145, A Derivative Of Human Cathelicidin Ll-37

The antimicrobial peptide OP-145 (1) was selected as template for the development of a therapeutic agent for coatings of implants due to its potent activity against diverse microbial species and its success in the treatment of patients with chronic otitis. The focus of our study is based on biophysical characterization of the interaction of OP-145 with bacterial and mammalian membrane mimetics, e.g. liposomes composed of phosphatidylglycerol and lipoteichoic acid as well as phosphatidylcholine. Similar to earlier findings on human cathelicidin LL-37 (2), OP-145 interacted with all lipid systems, but exhibited different incorporation mechanisms into the lipid bilayer. Thermodynamic and structural studies revealed the formation of disk-like aggregates in mammalian mimics and induction of a quasi-interdigitated structure in bacterial mimics. In agreement with in vitro studies these results indicate limited ability to distinguish bacterial from eukaryotic membranes. In order to improve selectivity of OP-145 we designed a new peptide by substitution of a single hydrophobic by a cationic amino acid residue in the hydrophobic face of OP-145. Comparable to earlier data using this strategy (3), the resulting peptide 1236-04 showed enhanced membrane selectivity in model systems inducing complete leakage of PG vesicles at very low concentrations, but none for PC. Surprisingly, peptide 1236-04 exhibited rather poor antimicrobial activity towards S. aureus and selected Gram-negative bacteria in vitro, but no toxicity in human dermal fibroblast. Differences in the interaction with other cell wall components may explain the discrepancy of findings between the model systems and living bacterial cells. Acknowledgement: This work was supported by FP7-HEALTH-2011, Biofilm Alliance. (1) Nell J.M. et al., Peptides 2006, 27:649-60. (2) Sevcsik E.et al., Biochim. Biophys. Acta 2007, 1768:2586-2595. (3) Huang J.F.et al., Pure Appl. Chem. (2010) 82:243-257.