Journal
PLOS ONE
Volume 6, Issue 4, Pages -Publisher
PUBLIC LIBRARY SCIENCE
DOI: 10.1371/journal.pone.0018550
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Funding
- NSF [MCB-0924124]
- Direct For Biological Sciences
- Div Of Molecular and Cellular Bioscience [0924124] Funding Source: National Science Foundation
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Plant defensins are small cysteine-rich antimicrobial proteins. Their three-dimensional structures are similar in that they consist of an alpha-helix and three anti-parallel beta-strands stabilized by four disulfide bonds. Plant defensins MsDef1 and MtDef4 are potent inhibitors of the growth of several filamentous fungi including Fusarium graminearum. However, they differ markedly in their antifungal properties as well as modes of antifungal action. MsDef1 induces prolific hyperbranching of fungal hyphae, whereas MtDef4 does not. Both defensins contain a highly conserved gamma-core motif (GXCX(3-9)C), a hallmark signature present in the disulfide-stabilized antimicrobial peptides, composed of beta 2 and beta 3 strands and the interposed loop. The gamma-core motifs of these two defensins differ significantly in their primary amino acid sequences and in their net charge. In this study, we have found that the major determinants of the antifungal activity and morphogenicity of these defensins reside in their gamma-core motifs. The MsDef1-gamma 4 variant in which the gamma-core motif of MsDef1 was replaced by that of MtDef4 was almost as potent as MtDef4 and also failed to induce hyperbranching of fungal hyphae. Importantly, the gamma-core motif of MtDef4 alone was capable of inhibiting fungal growth, but that of MsDef1 was not. The analysis of synthetic gamma-core variants of MtDef4 indicated that the cationic and hydrophobic amino acids were important for antifungal activity. Both MsDef1 and MtDef4 induced plasma membrane permeabilization; however, kinetic studies revealed that MtDef4 was more efficient in permeabilizing fungal plasma membrane than MsDef1. Furthermore, the in vitro antifungal activity of MsDef1, MsDef1-gamma 4, MtDef4 and peptides derived from the gamma-core motif of each defensin was not solely dependent on their ability to permeabilize the fungal plasma membrane. The data reported here indicate that the gamma-core motif defines the unique antifungal properties of each defensin and may facilitate de novo design of more potent antifungal peptides.
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