Thionins: properties, possible biological roles and mechanisms of action

Abstract

Thionins are low-molecular-weight proteins (M(r) ca. 5000) occurring in seeds, stems, roots and leaves of a number of plant species. The different members of this family of plant proteins show both sequence and structural homology, and are toxic to bacteria, fungi, yeasts and various naked cells in vitro. Toxicity requires an electrostatic interaction of the positively charged thionin with the negatively charged phospholipids making up the membrane, followed by either pore formation or a specific interaction with a certain lipid domain. This domain might be composed of phosphoinositides, which mediate transduction of environmental signals in eukaryotes. Their in vitro toxicity to plant pathogenic bacteria and fungi could reflect a direct role in plant defence, although, in view of the many divergent activities displayed by thionins both in vitro and in vivo, a biological role other than inhibition of microbial growth is equally plausible.

Interaction of wheat α‐thionin with large unilamellar vesicles

“…This modification diminished the positive charges of the molecule and led to the loss of toxicity to mice or yeast. In fact, all thionins exhibiting antimicrobial activity have a net positive charge at neutral pH (Florack & Stiekema, 1994).…”

“…This is also the case for Pyrularia thionin (Gasanov et al, 1993;Huang et al, 1997) and for a-hordothionin (Thevissen et al, 1996), where the interaction of the peptide with model membranes triggers the formation of nonbilayer structures or the collapse of planar lipid bilayers. The amphipatic nature of the surface of a-thionin (Florack & Stiekema, 1994) could be the underlying force directing these events.…”

“…Apart from this toxicity, which could reflect a direct role in plant defence, many other biological activities have been observed (Florack & Stiekema, 1994) and, therefore, their biological role is still a matter of controversy. It is thought that most, if not all, of these effects are the consequence of their interaction with the target-cell membrane (Carrasco et al, 1981).…”

The Cytotoxic Plant Protein, β-Purothionin, Forms Ion Channels in Lipid Membranes

“…However, their action at this site is still under debate. Thionins are toxic to a wide range of cells, and nearly every organism tested has proven to be susceptible (8,13). This universal toxicity suggests that the manner in which thionins kill cells does not rely on a specific cell surface receptor and that the processes disrupted by thionins are common to most cells.…”

Transgenic Phalaenopsis plants with resistance to Erwinia carotovora produced by introducing wasabi defensin gene using Agrobacterium method

“…So far, many antimicrobial proteins such as chitin-binding proteins, thionins, lipid-transfer proteins and defensins have been identified and their activity has been tested against fungi and bacteria (Florack and Stiekema 1994;Terras et al 1995).…”