Thionins: properties, possible biological roles and mechanisms of action

• Published in: Plant molecular biology 1994-10, Vol.26 (1), p.25-37
• Main Authors: Florack, D.E.A, Stiekema, W.J
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; antibacterial properties; antifungal properties; cell membranes; defense mechanisms; literature reviews; Models, Molecular; Molecular Sequence Data; phosphatidylinositols; phosphoinositides; phytotoxins; plant pathogens; Plant Proteins - chemistry; Plant Proteins - genetics; Plant Proteins - physiology; Plant Proteins - toxicity; plants; sulfur proteins; Toxins, Biological - chemistry; Toxins, Biological - genetics; Toxins, Biological - metabolism; Toxins, Biological - toxicity
• ISSN: 0167-4412; 1573-5028
• DOI: 10.1007/bf00039517

Thionins are low-molecular-weight proteins (Mr 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 toxicitv 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.