Phalloidin

Phalloidin is a toxin produced by several poisonous mushrooms, most notably Amanita phalloides (the death cap). It belongs to the phallotoxin family and is one of the peptide toxins associated with Amanita species. Phalloidin is of interest in biochemistry and cell biology because of its specific interaction with the cytoskeleton.

Phalloidin is a cyclic peptide that binds with high affinity to filamentous actin (F-actin). Upon binding, it stabilizes actin filaments and prevents their depolymerization, effectively locking actin in place. This stabilization disrupts normal actin turnover and cytoskeletal dynamics, which can impair cellular processes such as division, vesicle trafficking, and morphology.

Toxicology and exposure are typically discussed in the context of mushroom poisoning. In humans, phalloidin contributes to toxicity but is generally less acutely dangerous than the related amatoxins, largely because it is less readily absorbed from the gastrointestinal tract. Nevertheless, ingestion of phalloidin-containing mushrooms can cause gastrointestinal symptoms and, in large doses, hepatic and renal effects. Laboratory exposure to phalloidin requires caution due to its potent actin-binding activity.

Applications and research use Centers on actin staining in fixed cells. Fluorescently labeled phalloidin conjugates are widely used to visualize F-actin structures in microscopy. Because phalloidin does not readily cross intact cell membranes, it is used on fixed and permeabilized specimens rather than live cells, providing a reliable marker for filamentous actin networks.