Squalene monooxygenase

671320775ENSG00000104549ENSMUSG00000022351Q14534P52019NM_003129NM_009270NP_003120NP_033296Squalene monooxygenase (also called squalene epoxidase) is an enzyme that uses NADPH and molecular oxygen to oxidize squalene to 2,3-oxidosqualene (squalene epoxide). Squalene epoxidase catalyzes the first oxygenation step in sterol biosynthesis and is thought to be one of the rate-limiting enzymes in this pathway. In humans, squalene epoxidase is encoded by the SQLE gene.Several eukaryote genomes lack a squalene monooxygenase encoding gene, but instead encode an alternative squalene epoxidase that catalyzes the oxidation of squalene. Squalene monooxygenase (also called squalene epoxidase) is an enzyme that uses NADPH and molecular oxygen to oxidize squalene to 2,3-oxidosqualene (squalene epoxide). Squalene epoxidase catalyzes the first oxygenation step in sterol biosynthesis and is thought to be one of the rate-limiting enzymes in this pathway. In humans, squalene epoxidase is encoded by the SQLE gene.Several eukaryote genomes lack a squalene monooxygenase encoding gene, but instead encode an alternative squalene epoxidase that catalyzes the oxidation of squalene. The canonical squalene monooxygenase is a flavoprotein monooxygenase. Flavoprotein monooxygenase form flavin hydroperoxides at the enzyme active site, which then transfer the terminal oxygen atom of the hydroperoxide to the substrate. Squalene monooxygenase differs from other flavin monooxygenases in that the oxygen is inserted as an epoxide rather than as a hydroxyl group. Squalene monooxygenase contains a loosely bound FAD flavin and obtains electrons from NADPH-cytochrome P450 reductase, rather than binding the nicotinamide cofactor NADPH directly. The alternative squalene epoxidase belongs to the fatty acid hydroxylase superfamily and obtains electrons from cytochrome b5. Inhibitors of squalene epoxidase have found application mainly as antifungal drugs: Since squalene epoxidase is on the biosynthetic pathway leading to cholesterol, inhibitors of this enzyme may also find application in treatment of hypercholesterolemia. In yeast Saccharomyces cerevisiae, squalene epoxidase is localized to both the endoplasmic reticulum and lipid droplets. Only the ER localized protein is active.