Linearized esculentin-2EM shows pH dependent antibacterial activity with an alkaline optimum.
Here the hypothesis that linearized esculentin 2EM (E2EM-lin) from Glandirana emeljanovi possesses pH dependent activity is investigated. The peptide showed weak activity against Gram-negative bacteria (MLCs ≥ 75.0 μM) but potent efficacy towards Gram-positive bacteria (MLCs ≤ 6.25 μM). E2EM-lin adopted an α-helical structure in the presence of bacterial membranes that increased as pH was increased from 6 to 8 (↑ 15.5-26.9%), whilst similar increases in pH enhanced the ability of the peptide to penetrate (↑ 2.3-5.1 mN m-1) and lyse (↑ 15.1-32.5%) these membranes. Theoretical analysis predicted that this membranolytic mechanism involved a tilted segment, that increased along the α-helical long axis of E2EM-lin (1-23) in the N → C direction, with -  < µH > increasing overall from circa - 0.8 to - 0.3. In combination, these data showed that E2EM-lin killed bacteria via novel mechanisms that were enhanced by alkaline conditions and involved the formation of tilted and membranolytic, α-helical structure. The preference of E2EM-lin for Gram-positive bacteria over Gram-negative organisms was primarily driven by the superior ability of phosphatidylglycerol to induce α-helical structure in the peptide as compared to phosphatidylethanolamine. These data were used to generate a novel pore-forming model for the membranolytic activity of E2EM-lin, which would appear to be the first, major reported instance of pH dependent AMPs with alkaline optima using tilted structure to drive a pore-forming process. It is proposed that E2EM-lin has the potential for development to serve purposes ranging from therapeutic usage, such as chronic wound disinfection, to food preservation by killing food spoilage organisms.
['Malik|Erum|E|', 'Phoenix|David A|DA|', 'Snape|Timothy J|TJ|', 'Harris|Frederick|F|', 'Singh|Jaipaul|J|', 'Morton|Leslie H G|LHG|', 'Dennison|Sarah R|SR|http://orcid.org/0000-0003-4863-9607']
D029845:Amphibian Proteins D000900:Anti-Bacterial Agents D023181:Antimicrobial Cationic Peptides D006094:Gram-Positive Bacteria D006863:Hydrogen-Ion Concentration D000072756:Protein Conformation, alpha-Helical
Linearized esculentin 2EM (E2EM-lin) α-Helical structure Preference for gram-positive bacteria Tilted peptide pH dependent with alkaline optimum