Phalloidin is a phallotoxin produced by death cap mushroom Amanita phalloides. It is a cyclic peptide, which interacts with actin and this was first identified in phalloidin-poisoned rats. It is a heptapeptide, cyclic in nature, with a crosslink between tryptophan at position 6 and cysteine at position 3. The side chain of amino acid 7 (γ-δ-dihydroxyleucine) in phalloidin, is accessible to modifications, through which fluorescently labelled phalloidin compounds can be produced.
Phalloidin interacts with polymeric actin, and not oligomeric or monomeric forms. This interaction leads to highly stabilized actin filaments, which resist depolymerization and disassembly. In rats, this toxin causes death due to liver hemorrhage, and cells show abnormal actin clustering. The affinity of phalloidin to actin is not significantly altered after derivatizing fluorescently labelled phalloidin compounds. These compounds can be used to study actin structure and organization within eukaryotic cells.
