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Molecules 2018, 23(2), 329; https://doi.org/10.3390/molecules23020329

Role of Cationic Side Chains in the Antimicrobial Activity of C18G

1
Department of Chemistry and Biochemistry, Rowan University, Glassboro, NJ 08028, USA
2
Thomas N. Bantivoglio Honors Concentration, Rowan University, Glassboro, NJ 08028, USA
3
Department of Molecular and Cellular Biosciences, Rowan University, Glassboro, NJ 08028, USA
These authors contributed equally to this work.
*
Author to whom correspondence should be addressed.
Received: 11 January 2018 / Revised: 23 January 2018 / Accepted: 1 February 2018 / Published: 4 February 2018
(This article belongs to the Special Issue Antimicrobial Peptides and Peptidomimetics)
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Abstract

Antimicrobial peptides (AMPs) have been an area of great interest, due to the high selectivity of these molecules toward bacterial targets over host cells and the limited development of bacterial resistance to these molecules throughout evolution. The peptide C18G has been shown to be a selective, broad spectrum AMP with a net +8 cationic charge from seven lysine residues in the sequence. In this work, the cationic Lys residues were replaced with other natural or non-proteinogenic cationic amino acids: arginine, histidine, ornithine, or diaminopropionic acid. These changes vary in the structure of the amino acid side chain, the identity of the cationic moiety, and the pKa of the cationic group. Using a combination of spectroscopic and microbiological methods, the influence of these cationic groups on membrane binding, secondary structure, and antibacterial activity was investigated. The replacement of Lys with most other cationic residues had, at most, 2-fold effects on minimal inhibitory concentration against a variety of Gram-positive and Gram-negative bacteria. However, the peptide containing His as the cationic group showed dramatically reduced activity. All peptide variants retained the ability to bind lipid vesicles and showed clear preference for binding vesicles that contained anionic lipids. Similarly, all peptides adopted a helical conformation when bound to lipids or membrane mimetics, although the peptide containing diaminopropionic acid exhibited a decreased helicity. The peptides exhibited a wider variety of activity in the permeabilization of bacterial membranes, with peptides containing Lys, Arg, or Orn being the most broadly active. In all, the antibacterial activity of the C18G peptide is generally tolerant to changes in the structure and identity of the cationic amino acids, yielding new possibilities for design and development of AMPs that may be less susceptible to immune and bacterial recognition or in vivo degradation. View Full-Text
Keywords: antimicrobial peptides; fluorescence; lipid binding; non-natural amino acids antimicrobial peptides; fluorescence; lipid binding; non-natural amino acids
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Kohn, E.M.; Shirley, D.J.; Arotsky, L.; Picciano, A.M.; Ridgway, Z.; Urban, M.W.; Carone, B.R.; Caputo, G.A. Role of Cationic Side Chains in the Antimicrobial Activity of C18G. Molecules 2018, 23, 329.

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