Biophysical Properties of CAY-1, a Novel Fungicidal Plant Saponin

A. J. De Lucca, M. S. Palmgren, T. E. Cleveland, T. J. Walsh

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Background: CAY-1, a plant saponin, is lethal to several medically and agriculturally important fungi. CAY-1 displays synergy with amphotericin B and itraconzaole against fungi. To elucidate its properties, we studied pH effect on CAY-1 activity and possible fungal wall and membrane binding sites. Methods: (1) pH effect was determined in buffers (pH 3.0 to 9.4). Germinated conidia (25 µl, 105/ml in 1% potato dextrose broth [PDB]) of Aspergillus flavus were added to CAY-1 (225 µl, final concentrations: 0-12.4 µg/ml per buffer type). Controls were germinated conidia (25µl) in the proper buffer (225µl). After incubation (30 min, 30° C) sample aliquots were spread on PDA plates, incubated overnight (30º C) and colonies enumerated. Three replicate experiments were performed (n =18). (2) Ergosterol (ERG) and cholesterol (CHOL) were dissolved in ethanol (1mg/2ml). Pantoea agglomerans lipopolysaccharide (LPS) and glucan (GLU) were placed in PBS (1mg/ml, pH 7.2). Compounds were diluted in PDB before assays. Diluted ERG or CHOL (200 µl) were added to CAY-1(200 µl, 37.2 µg/ml in PDB) with final molar ratios of 1:1, 2:1, and 4:1 (compound: CAY-1). GLU and LPS were added to CAY-1 to give final weight ratios of 16:1, 33:1, and 66:1 (compound: CAY-1). All mixtures were incubated (15 and 45 min, 30° C). Next, germinated conidia (25 µl) of A. flavus were added to mixture aliquots (225 µl) and 225µl PDB (control). Bioassays were performed as above (n= 12). Results: (1) A significant (p

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    • ICAAC 42nd