Oxidosqualene cyclase

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Oxidosqualene cyclases (OSC) are enzymes involved in cyclization reactions of 2,3-oxidosqualene to form sterols or triterpenes.[1] There are two major groups of sterol-producing OSC enzymes:

Sterols and triterpenes are extremely diverse classes of natural products, particularly in plants, which often contain numerous OSC enzymes with different substrate and product specificities;[1] common examples include lupeol synthase and beta-amyrin synthase.[2] OSC enzymes' catalytic mechanism is similar to the prokaryotic squalene-hopene cyclase.[3]

Directed evolution and protein design have been used to identify small numbers of point mutations that alter the product specificities of OSC enzymes, most notably in altering a cycloartenol synthase to produce predominantly lanosterol.[4]


  1. ^ a b Thimmappa, Ramesha; Geisler, Katrin; Louveau, Thomas; O'Maille, Paul; Osbourn, Anne (29 April 2014). "Triterpene Biosynthesis in Plants". Annual Review of Plant Biology. 65 (1): 225–257. doi:10.1146/annurev-arplant-050312-120229. PMID 24498976. 
  2. ^ Sawai, S. (15 March 2006). "Plant Lanosterol Synthase: Divergence of the Sterol and Triterpene Biosynthetic Pathways in Eukaryotes". Plant and Cell Physiology. 47 (5): 673–677. doi:10.1093/pcp/pcj032. 
  3. ^ Wendt, KU; Poralla, K; Schulz, GE (19 September 1997). "Structure and function of a squalene cyclase". Science. 277 (5333): 1811–5. doi:10.1126/science.277.5333.1811. PMID 9295270. 
  4. ^ Lodeiro, Silvia; Schulz-Gasch, Tanja; Matsuda, Seiichi P. T. (October 2005). "Enzyme Redesign: Two Mutations Cooperate to Convert Cycloartenol Synthase into an Accurate Lanosterol Synthase". Journal of the American Chemical Society. 127 (41): 14132–14133. doi:10.1021/ja053791j. PMID 16218577.