Oxidosqualene cyclase involved in the biosynthesis of the highly oxygenated tetracyclic triterpenes mogrosides and cucurbitacins (PubMed:29192442, PubMed:25759326). Converts oxidosqualene to cucurbitadienol (PubMed:29192442, PubMed:25759326). (S)-2,3-epoxysqualene = cucurbitadienol Cucurbitadienol has anti-inflammation, anti-cancer activities, and acts as a precursor of traditional Chinese medicine active ingredients mogroside and cucurbitacin. Belongs to the terpene cyclase/mutase family.