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United States Department of Agriculture

Agricultural Research Service

Title: D-Cecropin B: Proteolytic Resistance, Lethality for Pathogenic Fungi, and Binding Properties

Authors
item DE Lucca Ii, Anthony
item Bland, John
item Jacks, Thomas
item Peter, Joann - NCI, POB, IHS
item Walsh, Thomas - NCI, POB, IHS

Submitted to: Journal of Medical and Veterinary Mycology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 8, 1999
Publication Date: N/A

Interpretive Summary: Aspergillus flavus is a naturally-occurring fungus that produces dangerous toxins on corn, cottonseed, and peanuts. We have found in earlier research that L-cecropin B, a natural peptide produced by the giant silk moth, kills Aspergillus flavus as well as other toxin-producing fungi at concentrations between 5 and 98 parts per million. Unfortunately, mature A. flavus cultures produce enzymes that destroys L-cecropin B. This fact reduces the possibility that this peptide could be used to combat mature cultures of this fungus. We synthesized a form of cecropin B (or D-amino acids) to determine whether this man-made peptide could withstand degrad- ation by A. flavus enzymes and yet retain the potent fungal-killing properties of the natural peptide. Research showed that the man-made D-cecropin B is not degraded by the A. flavus enzymes or other potent enzymes even after 2 hours of incubation. It also killed A. Flavus as well as the natural form of peptide. D-cecropin B was found to bind to compounds present in the fungal spores, thus suggesting the D-cecropin B attached to the surface of the spores or hyphae. It is possible that D-cecropin B could be used to combat fungal infections in plants, animals, and humans.

Technical Abstract: L-cecropin B (LCB) is a potent fungicidal peptide that is subject to proteolytic degradation by extracellular enzymes produced by Aspergillus flavus. We hypothesized that D-cecropin B (DCB), containing all D-amino acids, would resist proteolysis while retaining its fungicidal and target specificities. DCB was synthesized by solid phase methods using Fmoc chemistry. In vitro, at pH 6.0, DCB achieved LD90 for the germinating conidia of A. flavus at 12.5 uM. It was highly lethal for A. fumigatus, producing a LD98 value at 3.1 uM. DCB was also highly lethal for the nongeminating and germinating conidia of F. moniliforme, producing LD98 values for both conidial types at 1.2 uM. It achieved a LD95 for the nongerminating conidia of F. oxysporum at 2.5 uM and LD98 for the germinating conidia at 1.2 uM. The values were similar to those previously reported for LCB. DCB was not active for the nongerminating conidia of the tested Aspergillus species. It was lethal for Candida albicans with a LD98 at 12.5 uM. Papain, trypsin, pepsin A, and S. aureus V8 protease degraded LCB but not DCB. Binding assays and circular dichroism showed DCB and LCB bound to cholesterol, ergosterol, B-1, 3-glucan, mannan, and chitin. DCB is a potent fungicidal peptide for pathogenic fungi which resists proteolytic enzymes.

Last Modified: 8/22/2014
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