Lanosterol Synthase - Biological Function

Biological Function

Catalysis of Lanosterol Formation: Lanosterol synthase catalyzes the conversion of (S)-2,3-epoxysqualene to lanosterol, a key four-ringed intermediate in cholesterol biosynthesis. Thus, it in turn provides the precursor to estrogens, androgens, progesterones, and glucocorticoids. In eukaryotes the enzyme is bound to the cytosolic side of the endoplasmic reticulum membrane. While cholesterol synthesis is mostly associated with eukaryotes, few prokaryotes have been found to express lanosterol synthase; it has been found as a soluble protein in Methylococcus capsulatus.

Catalysis of Epoxylanosterol Formation: Lanosterol synthase also catalyzes the cyclization of 2,3;22,23-diepoxysqualene to 24(S),25-epoxylanosterol, which is later converted to 24(S),25-epoxycholesterol. Since the enzyme affinity for this second substrate is greater than for the monoepoxy (S)-2,3-epoxysqualene, under partial inhibition conversion of 2,3;22,23-diepoxysqualene to 24(S),25-epoxylanosterol is favored over lanosterol synthesis. This has relevance for disease prevention and treatment (see Disease Relevance, below).