Amanita phalloides - the death cap, dangerous mushroom but also a molecular biology tool

Possibly the most poisonous species of mushroom found in Europe, the pleasant-tasting death cap is responsible for the majority of deaths caused by mushroom consumption. Early symptoms include abdominal pain and diarrhoea which pass after 2-3 days. Death occurs at least 6 days after ingestion, often by liver failure.

A prominent class of toxins involved in this are the amatoxins, which are proteins consisting of an 8-peptide ring structure. They work by binding and inhibiting RNA polymerase II, the enzyme responsible for transcription and the production of messenger RNA (this is the precursor process to protein synthesis). By ceasing protein synthesis, the entire metabolism of affected cells is effectively blocked - causing the liver to disintegrate (usually the first organ to encounter the toxin in digestion).

Related to the amatoxins are the phallotoxins, 7-peptide double-ring-structured proteins also produced by the death cap. One of these, phalloidin, functions as a toxin by binding and stabilising an important cytoskeletal component of the cell - F actin. It is the dynamic polymerisation and depolymerisation of actin (building chains and breaking them again to form F and G actin respectively) which is relied upon for essential functions such as signalling and movement of organelles within the cell.
Due to its binding of F actin, phalloidin derivatives are used in cell microscopy to label F actin using attached fluorescent tags.

[Picture from Really Clever co-founder Matt Millar]