To provide insights into the structure-function relationships of oxidosqualene-lanosterol cyclase (ERG7) from Saccharomyces cerevisiae, the Phe699 was exchanged against hydrophilic polar uncharged residues Ser, Thr, Cys, Gln, and Tyr to characterize its product profile and functional role in ERG7 activity. Among the substitutions, only the ERG7F699T mutant produced novel protosta-13(17),24-dien...