title: D-cecropin B: proteolytic resistance, lethality for pathogenic fungi and binding properties.
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 x 0, DCB was lethal against the germinating conidia of A. flavus (LD90, 25 microM) and A. fumigatus (LD98, 25 microM) and for nongerminating and germinating conidia of Fusarium moniliforme (LD98, 1 x 25 microM) and F. oxysporum (LD95, 2 x 5 microM) at concentrations similar to those previously reported for LCB. It was lethal for Candida albicans with an LD98 at 12 x 5, microM. DCB was not active for the nongerminating conidia of A. fumigatus or A. flavus. 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, beta-1,3-glucan, mannan and chitin. Data show that DCB retains the potent fungicidal properties of the L-form while being resistant to proteolytic enzymes that degrade the latter peptide. This study demonstrates that D-enantiomerization of cecropin B yields a novel fungicidal peptide, which resists proteolytic degradation and is lethal for pathogenic fungi.
authors.affiliation: Southern Regional Research Center, USDA, ARS, New Orleans, LA 70124, USA. adelucca@nola.srrc.usda.gov
authors.forename: A J
authors.initials: AJ
authors.lastname: De Lucca
authors.forename: J M
authors.initials: JM
authors.lastname: Bland
authors.forename: C B
authors.initials: CB
authors.lastname: Vigo
authors.forename: T J
authors.initials: TJ
authors.lastname: Jacks
authors.forename: J
authors.initials: J
authors.lastname: Peter
authors.forename: T J
authors.initials: TJ
authors.lastname: Walsh
mesh_terms: D000935:Antifungal Agents / Q000494:pharmacology*; D001230:Aspergillus / Q000187:drug effects; D002176:Candida albicans / Q000187:drug effects; D002473:Cell Wall / Q000378:metabolism; D004875:Ergosterol / Q000378:metabolism; D005670:Fusarium / Q000187:drug effects; D019476:Insect Proteins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D010455:Peptides / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D011485:Protein Binding; D013237:Stereoisomerism
chemical_list: D000935:Antifungal Agents; D019476:Insect Proteins; D010455:Peptides; C031162:cecropin B protein, Insecta; D004875:Ergosterol