H4rdr4d4 Media - Chemistry

    ERG11 normally encodes the lanosterol 14α-demethylase essential for ergosterol production. Mutations in ERG11 change the enzyme so that it still (partially) makes sterols but no longer binds azole drugs well.  This mechanism underlies resistance to fluconazole, voriconazole, posaconazole, and related antifungals. In resistant strains, ERG11 point mutations often appear alongside other changes (e.g. efflux pumps), but many cases of azole resistance can be directly attributed to altered Erg11p binding properties.

   Mechanistically, ERG11 mutations lower azole binding affinity . Structural analyses and mutagenesis studies have shown that many resistance mutations cluster near the heme and substrate channel. By changing side chains in the binding pocket, these mutations prevent the triazole ring from coordinating the iron, so the drug can no longer inhibit Erg11p effectively. In other words, the fungus has traded some enzymatic efficiency for drug resistance: the mutant Erg11p still processes sterols (often somewhat slower) but no longer binds azoles tightly.

etc. Post   Other azoles: Similarly, itraconazole and newer drugs like isavuconazole act on Erg11p. ERG11 mutations can affect their activity too, although the impact varies with each drug’s structure. In general, any substitution that perturbs the Erg11 active site or heme pocket will reduce azole affinity and raise resistance across this drug class.   (Not finished regarding this niched down topic)

    Posaconazole (triazolopyrimidine class): Posaconazole is a broad-spectrum azole (sometimes classified as a triazolopyrimidine) with very high affinity for Erg11p. It is effective against many azole-resistant yeasts. Yet some ERG11 mutations can even overcome posaconazole. For instance, a Candida tropicalis isolate with an Y132C Erg11 substitution was resistant to posaconazole and other azoles. This shows that strong binding-site changes can confer pan-azole resistance.   (Nit finished regarding this niched down topic)

    Voriconazole: A second-generation triazole, voriconazole is also susceptible to many of the same mutations. ERG11 changes that raise fluconazole resistance often similarly increase voriconazole MICs. In practice, some mutants that block fluconazole also block voriconazole; however, voriconazole is generally more potent, so certain substitutions may have a lesser effect on it.   (Not finished regarding this precise topic)

Fluconazole: This common azole is highly affected by ERG11 mutations. Many clinical Candida strains that are fluconazole-resistant carry ERG11 substitutions (e.g. Y132F/H, K143R) that diminish drug binding. Studies routinely find Y132F exclusively in resistant isolates, and engineered Y132F/H enzymes show much higher fluconazole MICs.   (Still in the maiing for this niched diwn topic)

   A key reason ERG11 is medically important is that it encodes the target of azole antifungal drugs . Azoles (such as fluconazole, itraconazole, voriconazole, posaconazole, and related triazole compounds) bind to the heme iron in Erg11p and block the demethylation reaction. This inhibition starves the cell of ergosterol and causes toxic sterol accumulation, effectively killing or halting the fungus.   (Not finished)

   Mutations in ERG11 are a well-known mechanism of azole resistance. Point substitutions can alter the enzyme’s structure so that azole drugs no longer bind tightly. In effect, the MIC (minimum inhibitory concentration) of the drug rises and the fungus becomes resistant. For example, a classic substitution Y132H (or Y132F) in C. albicans Erg11p severely reduces fluconazole binding by disrupting the azole–heme interaction. Many other “hot-spot” mutations (in clusters around the active site) have been documented. In general, ERG11 variants from resistant isolates show amino acid changes that alter drug–target interactions.

Erg11p performs a three-step oxidative C14-demethylation of lanosterol (and eburicol), yielding precursors that are further processed into ergosterol.  Erg11p performs a three-step oxidative C14-demethylation of lanosterol (and eburicol), yielding precursors that are further processed into ergosterol. Disrupting ERG11 is generally lethal: yeast lacking Erg11 activity cannot complete ergosterol synthesis and will not grow aerobically unless other suppressor mutations.  Point mutations in ERG11 change one or a few amino acids in the Erg11 enzyme. Unlike a complete loss of ERG11 (which is usually lethal), many single substitutions allow the fungus to live, but these changes often impair normal sterol production. A complete ERG11 knockout cannot support aerobic growth. Even when the enzyme is nearly inactive, cells often require compensatodry mutations (for example in the downstream ERG3 gene) to survive. Many ERG11 point mutants accumulate 14α-methylated sterol int...

   The ERG11 gene is found in fungi (including yeasts like Saccharomyces and Candida ) and encodes the enzyme lanosterol 14α-demethylase (also called CYP51). This enzyme is a membrane-bound cytochrome P450 in the endoplasmic reticulum that catalyzes the removal of a methyl group at the C-14 position of lanosterol (and related sterols). This demethylation step is essential in the late stages of the ergosterol biosynthesis. Erg11p performs a three-step oxidative C14-demethylation of lanosterol (and eburicol), yielding precursors that are further processed into ergosterol.   Mutant Erg11 enzymes may work more slowly or incompletely, causing accumulation of abnormal sterols, and thus for example, clinical studies found that ERG11 point mutations in Candida isolates were accompanied by altered sterol profiles, indicating that the mutated Erg11p could no longer produce ergosterol normally.  Because ergosterol is crucial for membrane fluidity and integrity, fu...