Ergosterol

Sterols are essential structural and regulatory components of eukaryotic cell membranes. Mammals, plants and fungi produce similar sterols, which differ in the number and location of double bonds and methyl side chains. Ergosterol (ergosta-5, 7, 22-trien-3β-ol) 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 the end product of the sterol biosynthetic pathway and is the major sterol in yeasts. Like cholesterol in mammalian cells, it is responsible for membrane fluidity and permeability^[6]. Ergosterol is a very important component of yeast and other fungal cell membranes, playing many important roles as that cholesterol plays in animal cells.^[1] Its specificity in higher fungi is thought to be related to the climatic instabilities (highly varying humidity and moisture conditions) encountered by these organisms in their typical ecological niches (plant and animal surfaces, soil). Thus, despite the added energy requirements of ergosterol synthesis (if compared to cholesterol), ergosterol is thought to have evolved as a nearly ubiquitous, evolutionarily advantageous fungal alternative to cholesterol.

Figure 1 the chemical structure of ergosterol

Since ergosterol is a key component in cell membranes of fungi, yet absent in those of animals. It has become a very useful target for antifungal drugs. Ergosterol is also present in the cell membranes of some protists, such as trypanosomes. This also becomes the basis for the use of some antifungals against West African sleeping sickness.
Antifungal drugs targeting ergosterol includes Amphotericin B^{[2, 3]}, fluconazole, miconazole, itraconazole, and clotrimazole. Amphotericin B acts by binding to sterols (ergosterol) in the cell membrane of susceptible fungi^{[2, 3]}. This creates a transmembrane channel, and the resultant change in membrane permeability allowing leakage of intracellular components. Ergosterol, the principal sterol in the fungal cytoplasmic membrane, is the target site of action of amphotericin B and the azoles. Amphotericin B, a polyene, binds irreversibly to ergosterol, resulting in disruption of membrane integrity and ultimately cell death^{[2, 3]}. Amphotericin B, though has been replaced by safer agents in most circumstances, is still used, despite its side effects, for life-threatening fungal or protozoan infections.
Fluconazole, miconazole, itraconazole, and clotrimazole work in a different way, take effect through inhibiting synthesis of ergosterol from lanosterol by interfering with14α-demethylase^{[4, 5]}. Fluconazole interacts with 14-α demethylase, a cytochrome P-450 enzyme necessary to convert lanosterol to ergosterol. As ergosterol is an essential component of the fungal cell membrane, inhibition of its synthesis results in increased cellular permeability causing leakage of cellular contents. Fluconazole may also inhibit endogenous respiration, interact with membrane phospholipids, inhibit the transformation of yeasts to mycelial forms, inhibit purine uptake, and impair triglyceride and/or phospholipid biosynthesis.

1. Ruzicka, S., Edgerton, D., Norman, M., & Hill, T. (2000). The utility of ergosterol as a bioindicator of fungi in temperate soils. Soil Biology & Biochemistry, 32(7), 989-1005.
2. Vertut-Croquin, A, et al. "Differences in the interaction of the polyene antibiotic amphotericin B with cholesterolor ergosterol-containing phospholipid vesicles. A circular dichroism and permeability study." Biochemistry 22.12(1983): 2939-44.
3. Baginski, M, H. Resat, and E. Borowski. "Comparative molecular dynamics simulations of amphotericin B-cholesterol/ergosterol membrane channels." Biochim Biophys Acta 1567.1-2(2002): 63-78.
4. Ballard, S. A., et al. "A novel method for studying ergosterol biosynthesis by a cell-free preparation of Aspergillus fumigatus and its inhibition by azole antifungal agents." J Med Vet Mycol 28.4(1990):335-344.
5. Lv, Quan-Zhen; Yan, Lan; Jiang, Yuan-Ying (2016). "The synthesis, regulation, and functions of sterols in Candida albicans: Well-known but still lots to learn". Virulence. 7 (6): 649–659.
6. Parks, L. W., Smith, S. J. & Crowley, J. H. (1995). Biochemical and physiological effects of sterol alterations in yeast – a review. Lipids 30, 227–230.

Ergosterol is a membrane component and with few exceptions is restricted to eumycotic fungi (101). As a constituent of intact membranes, its abundance should reflect the amount of living fungal biomass in an environment. This membrane component has been related to biomass by a number of investigators and the values range from 1.9 to 11.5 mg ergosterol g?1 mycelium (102). These conversion factors yield very high values for fungal biomass, and seem unrealistic (102) when compared with independent measures of bacterial biomass. It is likely that the ergosterol assay detects nonliving hyphae and these measures may overestimate viable fungal biomass. Similarly, chitin is a dominant cell wall component in most fungi and has been proposed as a unique marker for total fungal biomass.

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Ergosterol is a steroid alcohol that when irradiated with ultraviolet light yields calciferol (vitamin d2). irradiated ergosterol is added to milk for vitamin d fortification.

Ergosterol may be used to study the function of anti-fungal drugs such as Amphotericin B and its analogues and to study the ergosterol biosynthesis pathway within various fungi. It acts as a useful indicator of living fungal biomass.

Most important of the provitamins D. Usually obtained from yeast which synthesizes it from simple sugars such as glucose. Vitamin (antirachitic).

ChEBI: A phytosterol consisting of ergostane having double bonds at the 5,6-, 7,8- and 22,23-positions as well as a 3beta-hydroxy group.

ergosterol: A sterol occurring infungi, bacteria, algae, and plants. It isconverted into vitamin D₂ by the actionof ultraviolet light.

Ergosterol or provitamin D2 is a biological precursor of Vitamin D2. It is found predominantly in cell membranes of fungi and protists such as trypanosomes.

Due to its ability to catalyze calcium deposition in the bony structure (thus preventing rickets), overdosage of vitamin D may be harmful.

Ergosterol has a role in maintaining the integrity of the cell membrane and its fluidity. The sterol has anti-tumor and anti-inflammatory properties.

Crystallise ergosterol from EtOAc, then from ethylene dichloride or EtOH/*C6H6 (3:1). It has been purified by conversion to the isobutyl ester which crystallises from Et2O/Me2CO (1:3) with m: turbid at 148o, melts at 159o and becomes clear at 162o, followed by hydrolysis, [Bill & Honeywell J Biol Chem 80 15 1938]. When crystallised from EtOH, it forms the 1.5-hydrate m 168o. The water is difficult to remove giving an amorphous solid m 166-183o, b 250o/high vacuum. It is light sensitive. The benzoate has m 169-171o, after crystallisation from Me2CO/*C6H6 (4:1) after prolonged standing at 0o and becomes highly charged, with [] D20 -177o (c 1, CHCl3). [UV of sterols: Hogness et al. J Biol Chem 120 239 1937, Beilstein 6 IV 4407.]