Ergosterol is a sterol found in fungi, and named for ergot, the common name of members of the fungal genus Claviceps from which ergosterol was first isolated. Ergosterol is a component of yeast and other fungal cell membranes, serving many of the same functions that cholesterol serves in animal cells. Its specificity in higher fungi is thought to be related to the climatic instabilities encountered by these organisms in their typical ecological niches. Thus, despite the added energy requirements of ergosterol synthesis, ergosterol is thought to have evolved as a nearly ubiquitous, evolutionarily advantageous fungal alternative to cholesterol.
Because ergosterol is present in cell membranes of fungi, yet absent in those of animals, it is a useful target for antifungal drugs. Ergosterol is also present in the cell membranes of some protists, such as trypanosomes. This is the basis for the use of some antifungals against West African sleeping sickness. Amphotericin B, an antifungal drug, targets ergosterol. It binds physically to ergosterol within the membrane, thus creating a polar pore in fungal membranes. This causes ions and other molecules to leak out, which will kill the cell. Amphotericin B has been replaced by safer agents in most circumstances, but is still used, despite its side effects, for life-threatening fungal or protozoan infections. Fluconazole, miconazole, itraconazole, clotrimazole, and myclobutanilwork in a different way, inhibiting synthesis of ergosterol from lanosterol by interfering with 14α-demethylase. Ergosterol is a smaller molecule than lanosterol; it is synthesized by combining two molecules of farnesyl pyrophosphate, a 15-carbon-long terpenoid, into lanosterol, which has 30 carbons. Then, two methyl groups are removed, making ergosterol. The "azole" class of antifungal agentsinhibit the enzyme that performs these demethylation steps in the biosynthetic pathway between lanosterol and ergosterol.
Target for antiprotozoal drugs
Some protozoa, including Trichomonas and Leishmania are inhibited by drugs that target ergosterol synthesis and function
As a vitamin D2 precursor
Ergosterol is a biological precursor of vitamin D2, the chemical name of which is ergocalciferol. Exposure to ultraviolet light causes a photochemical reaction that converts ergosterol to ergocalciferol. This happens naturally to a certain extent, and many mushrooms are irradiated after harvest to increase their vitamin D content. Fungi are also grown industrially so that ergosterol can be extracted and converted to Vitamin Dfor sale as a dietary supplement and food additive. Preparations of irradiated ergosterol containing a mixture of previtamin and vitamin D2 were called Viosterol in the 1930s.
