PHALLOIDIN

Description

Phalloidin is a natural mycotoxin first isolated from the death cap mushroom, A. phalloides. It binds F-actin and stabilizes actin fibers. Fluorescently labeled phalloidin is commonly used to stain F-actin in cells.

Chemical Properties

white powder

Uses

Phalloidin has been used:

• As a supplement in PEM buffer and dimethyl sulfoxide (DMSO).
• As a drug.
• In immunohistochemistry to stain F-actin.

Definition

ChEBI: A homodetic bicyclic heptapeptide having a sulfide bridge.

General Description

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 labeled phalloidin compounds can be produced.

Safety Profile

Poison by ingestion, intraperitoneal, and intravenous routes. Mutation data reported. Whenheated to decomposition it emits toxic fumes of SOx, and NOx.

Enzyme inhibitor

This bicyclic heptapeptide toxin (FW = 788.88 g/mol; CAS 17466-45-4) is was first isolated from the poisonous green fungus Amanita phalloides. Primary Mode of Action: Phalloidin binds preferentially to filamentous actin; little or no binding to globular actin has been detected. such preferential action stimulates actin polymerization, and phalloidin lowers the actin monomer critical concentration by 30x, from 50-100 nM down to 2-3 nM. When present at 1 to 10 concentration ratio of phalloidin to total actin subunits, actin filaments are also greatly stabilized toward depolymerization. Effects on Actin Filaments: Cellular processes requiring filament disassembly are likewise inhibited. Depolymerization of F-actin by cytochalasins, potassium iodide, and elevated temperatures are inhibited by phalloidin binding. Because the toxin and its fluorescent derivatives are relatively small, a wide variety of actin-binding proteins can still bind to phalloidin-labeled filamentts. Perhaps more significantly, phalloidin-labeled actin filaments retain many of their functional properties, such that phalloidin-labeled, glycerinated muscle fibers can still contract, and labeled actin filaments still move on myosin that has been tethered to solid-phase substrates. Phalloidin can be also be used to assess the relativeconcentrations of these two forms of actin as well as a means to label actin filaments in a cell (See Phallacidin).