The catalytic cavity of the Alicyclobacillus acidocaldarius squalene–hopene cyclase is predominantly lined by aromatic amino acids. In mutant cyclases, the four tyrosine residues in the catalytic cavity were replaced by different amino acids. The mutants showed significant differences in catalytic behavior compared to the wild-type and to each other. Mutants Y609L, Y609C and Y609S produced the bicyclic main product γ-polypodatetraene, while Y495L and Y612L showed a wild-type product pattern and produced hopene as the main product. Altered product patterns were also found with Y420 mutations.
