Alteration of the substrate's prefolded conformation and cyclization stereochemistry of oxidosqualene-lanosterol cyclase of Saccharomyces cerevisiae by substitution at phenylalanine 699.

The Saccharomyces cerevisiae ERG7(Phe699) mutants produced one chair-chair-chair (C-C-C) and two chair-boat-chair (C-B-C) truncated tricyclic compounds, one tetracyclic 17alpha-exocyclic unrearranged intermediate, and two 17beta-exocyclic truncated rearranged intermediates. These results provided direct evidence for the importance of the residue in affecting mechanistic transitions between C-B-C and C-C-C substrate conformation and between the 17alpha- and 17beta-exocyclic side chain stereochemistry as well as in stabilizing the 6-6-5 tricyclic and the protosteryl C-17 cations.