Design, synthesis and characterization of antifungal peptides derived from the sequence of two thistle flowers defensins

FERNANDEZ, A; MALBRÁN, I; VAIRO CAVALLI, S; BAKÁS, L; GUZMÁN, F; CURTO L.M.; MATÉ, S; VÁZQUEZ, R

Congreso; XLVII Reunión Anual de la Sociedad Argentina de Biofísica; 2018

Plant defensins and defensin-like (DEFL) proteins are small basic, cysteine-rich proteins ubiquitously expressed in the plant kingdom and mostly involved in host defence. They present a highly variable sequence but a conserved structure. Sequence diversity appears to be correlated with differential functions exhibited (antifungal and antimicrobial, among others). Two highly conserved regions have been identified among plant defensins, which are important for their activity: the g-core located in the C-terminal region with a β hairpin structure and the α-core located in the N-terminal region. The importance of these motifs lies in the presence of positive residues which would allow the interaction with negative charges on the pathogen membrane and/or cell wall. In this work, potential antifungal peptides were designed from these regions, through the use of bioinformatic tools and using as template the sequence of two defensins (DefSm1D and DefSm2) of Silybum marianum (L.) Gaertn. previously cloned from thistle flowers. Five peptides were synthesized, from DefSm1D sequence: 3243, 3245 and 3246; and from DefSm2:3248 and 3250. Then, peptides were purified and characterized by HPLC-RP, MALDI-TOF-MS and CD. Their activity against the phytopathogenic fungus Fusarium graminearum Schwabe, their surface-active properties, as well as the ability to exclude the membrane-impermeable dye propidium iodide (PI) of conidia after treatment with the peptides were assessed. Peptides 3248 and 3250 were active against F. graminearum at micromolar concentration and produced PI uptake on conidia. The present work contributes to the knowledge of defensins, which are defense cysteine-rich proteins present in S. marianum flowers, which grows in Argentina as a wild weed naturally resistance to fungal pathogens.