Mode of action of the antimicrobial peptide D4E1 on Aspergillus flavus

Authors: MOORE, JOCELYN - University Of Louisiana At Lafayette; Rajasekaran, Kanniah - Rajah; Cary, Jeffrey; CHLAN, CARYL - University Of Louisiana At Lafayette

Submitted to: International Journal of Peptide Research and Therapeutics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2018
Publication Date: 9/27/2018
Citation: Moore, J., Rajasekaran, K., Cary, J.W., Chlan, C. 2018. Mode of action of the antimicrobial peptide D4E1 on Aspergillus flavus. International Journal of Peptide Research and Therapeutics. 25(3):1135-1145. https://doi.org/10.1007/s10989-018-9762-1.
DOI: https://doi.org/10.1007/s10989-018-9762-1

Interpretive Summary: D4E1 is a synthetic peptide (small protein) that has broad spectrum antimicrobial activity including inhibition of Aspergillus (A.) flavus. A. flavus is a mold that also produces a group of compounds known as aflatoxins that are mutagenic and carcinogenic when consumed. We have been studying mechanisms to control the growth of A. flavus in crop plants and D4E1 is a promising candidate control agent. The mechanism of action of this synthetic peptide is unknown. Studies showed that D4E1 permeabilizes (produces pores) cell membranes of A. flavus and allows entry of small molecules of less than 3,000 daltons (a unit of size) but not molecules larger than 10,000 daltons. In addition, concentrations of 1 micromolar D4E1 induced a stress response by the mold and likely the initiation of cell death. Based on these studies, it appears that D4E1 acts to harm the mold through pore formation in membranes and induction of cell death due to accumulation of compounds that cause stress in the mold.

Technical Abstract: The synthetic, linear peptide, D4E1, demonstrates antimicrobial activity against a broad spectrum of organisms including the toxigenic filamentous Ascomycete, Aspergillus flavus with a minimal lethal concentration of 12.5 µM against germinating conidia. However, the mechanism associated with the antimicrobial properties of D4E1 has not been studied in detail. Here we demonstrate that D4E1 permeabilizes mycelial membranes through monitoring cellular infiltration of SYTOX Green dye, a nucleic acid intercalating agent that can only enter cells through compromised membranes. The membrane lesions resulting from treatment with D4E1 allowed translocation into cells of 3,000 Da dextran-fluorescein conjugates but not 10,000 Da conjugates. In addition to permeabilizing membranes, treatment with D4E1 at concentrations as low as 1 µM induced the accumulation of reactive oxygen species (ROS) in germinating A. flavus conidia. ROS accumulation is associated with stress response and initiation of apoptosis. Thus, the antimicrobial activity of D4E1 likely results from membrane permeabilization and accumulation of ROS which induces apoptotic events.