Figure 4.
The biosynthesis of cholesterol: a paradigmatic isoprenoid pathway. Crystal structures of key enzymes in the pathway have been solved, including farnesyl pyrophosphate synthase (gold; PDB: 1RQI), squalene synthase (light blue; PDB: 3WEG), and oxidosqualene-lanosterol cyclase (magenta; PDB 1W6K). These crystal structures provide opportunities to predict functions of related enzymes of the isoprenoid synthase superfamily. However, function prediction for the terpenoid synthases (also called terpene cyclases) is extremely challenging due to the huge product chemical space created by carbocation rearrangements.