What is ergosterol and why is it a drug target?

• A. Ergosterol is a key fungal membrane component; many antifungals target its synthesis or function.
• B. Ergosterol is a bacterial membrane component; antifungals block its synthesis.
• C. Ergosterol is a plant sterol; antifungals modify plant membranes.
• D. Ergosterol is a viral lipid; antifungals disrupt its packaging.

Answer: (A)

Ergosterol is the main sterol in fungal cell membranes, serving a role similar to cholesterol in human membranes. This makes it a prime drug target because disrupting ergosterol synthesis or function weakens the fungal membrane while leaving human cells relatively unharmed.

Many antifungals exploit this difference. Drugs like azoles block the enzyme that converts a precursor into ergosterol, lowering ergosterol levels and causing buildup of intermediate sterols that destabilize the membrane. Other drugs, such as allylamines, inhibit a step earlier in the pathway, also reducing ergosterol production. Then there are polyenes that bind directly to ergosterol in the membrane and form pores, leaking ions and other cellular contents which kills the cell. Because humans don’t synthesize ergosterol, this selective targeting tends to affect fungi more than human cells, though some toxicity can occur.

The other statements miss the mark: bacteria don’t rely on ergosterol in their membranes, and plants use different sterols; ergosterol isn’t a viral lipid.