Antifungal effects and mechanism of action of viscotoxin A₃

Abstract

Viscotoxins are cationic proteins, isolated from different mistletoe species, that belong to the group of thionins, a group of basic cysteine‐rich peptides of ≈ 5 kDa. They have been shown to be cytotoxic to different types of cell, including animal, bacterial and fungal. The aim of this study was to obtain information on the cell targets and the mechanism of action of viscotoxin isoform A3 (VtA3). We describe a detailed study of viscotoxin interaction with fungal‐derived model membranes, its location inside spores of Fusarium solani, as well as their induced spore death. We show that VtA3 induces the appearance of ion‐channel‐like activity, the generation of H2O2, and an increase in cytoplasmic free Ca2+. Moreover, we show that Ca2+ is involved in VtA3‐induced spore death and increased H2O2 concentration. The data presented here strongly support the notion that the antifungal activity of VtA3 is due to membrane binding and channel formation, leading to destabilization and disruption of the plasma membrane, thereby supporting a direct role for viscotoxins in the plant defence mechanism.

Anomalous diffusion and dynamical correlation between the side chains and the main chain of proteins in their native state

“…Because the loops and the N and C-terminal parts are more flexible, the sidechain motions and main-chain motions are strongly correlated in this collective motion. This collective motion could contribute to the biological function of VA3, which is still poorly understood (31).…”

Nutrient composition of mistletoe (Viscum album) and its nutritive value for ruminant animals

“…Among these, lectin (Pryme et al 2006) and agglutinin (Hajto et al 1999) are shown to have cytostatic and immunmodulatory properties via suppressing tumour growth at the transcriptional level as well as potentiating the activity of tumour necrosis factor alpha to induce apoptosis and stabilize DNA in cancer therapy. Viscotoxin (Giudici et al 2006;Liu et al 2006) and thionin (Stec 2006) have cytotoxic properties to protect plant tissue. Other effects of the mistletoe extracts have also been shown, which may broadly include immunostimulant effects through enhancing phagositosis and extracellular burst activity of leukocytes (Dugenci et al 2003), neurophysiolgical action to increase intestinal contractility through activating muscarinic receptors (Radenkovic et al 2006), and hypoglycaemic properties through an unknown mechanism (Ohiri et al 2003).…”

An Expressed Sequence Tag Analysis for the Fast-Growing Shoots of Bambusa edulis Murno

“…This means that thionin must be expressed only in a specific period of time, e.g., during shoot growth. It is supposed that thionin could have a function as a protective peptide in soft regions against predators or pests, as viscotoxins or thionins found from Viscum album (Holtorf et al 1998;Giudici et al 2006). Ethylene is responsible for seed germination, root initiation, growth, floral differentiation, initiation of fruit ripening, senescence, dormancy, sex differentiation, and responding to environment stresses.…”