The cysteine 703 to isoleucine or histidine mutation of the oxidosqualene-lanosterol cyclase from Saccharomyces cerevisiae generates an iridal-type triterpenoid

► Oxidosqualene cyclases catalyze the conversion of oxidosqualene into diverse sterols and triterpenoids. ► An iridal-type triterpenoidin conjunction of numerous intermediates was produced by ERG7C703 mutants. ► The functional role of ERG7C703 is involved in stabilizing the bicyclic C-8 cation and the rearranged intermediate.