Figure 6. Geosmin synthase.

Geosmin synthase is a bifunctional enzyme with αα domain architecture that catalyzes FPP cyclization in the N-terminal domain (blue) to generate germacrene D and germacradienol, the latter of which undergoes a cyclization and fragmentation reaction in the C-terminal domain (green) to yield geosmin and acetone. The structure of the N-terminal domain was determined by X-ray crystallographic methods, and the structure of the C-terminal domain was generated through homology modeling. The domain assembly shown is based on the best fit of small-angle X-ray scattering data (the 41-residue interdomain linker is not shown).⁵⁰