Submitted to: Journal of Medical and Veterinary Mycology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/13/2000
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 produces 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 having synthetic (D-cecropin B) to determine whether this synthetic peptide could withstand degradation by A. flavus enzymes and yet retain the fungal-killing properties of the natural peptide. Research showed that the synthetic 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 did the natural form of the peptide. D-cecropin B was found to bind to compounds present in the fungal spores, thus suggesting that D-cecropin B attaches 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, should 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 was lethal for the germinating conidia of A. flavus, and A. fumigatus and for nongerminating and germinating conidia of Fusarium moniliforme and F. oxysporum at concentrations 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 LC 98 at 12.5 uM. Papain, trypsin, pepsin A, and Staphylococcus 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 degradation by proteolytic enzymes.