This is the crystal structure of an extracellular phytase enzyme from the fungi, Aspergillus ficuum. This enzyme hydrolyses phytate (myo-inositol-hexakisphospate), the primary storage form of phosphorus in plant seeds and pollen. Phytases can also have non-specific phosphorus monoester activity.

This phytase is a monomer with two domains, an alpha domain and an alpha/beta domain. The active site is in an indentation between these domains. The indentation is closed off at the back by an N-terminal lid. Basic amino acids at the active site help bind the negatively charged 3-phosphorus group on phytate. It is thought that a histidine (59) makes the nucleophilic attack on the phosphorus group and an aspartate (339) provides the proton for the leaving alcohol.

Kostrewa, D., F. Gruninger-Leitch, A. D’Arcy, C. Broger, D. Mitchell, A.P.G.M. van Loon, 1997. “Crystal structure of phytase from Aspergillus ficuum at 2.5 Å resolution. Nature Structural Biology 4:185-190.
Vincent, J.B., M.W. Crowder, B.A. Averil. 1992. “Hydrolysis of phosphate monoesters: a biological problem with multiple chemical solutions.” Trends in Biochemical Science 17:105-110.

This page was constructed by L. Ward Good as a class project for “Mineral Nutrition of Plants”, SoilSci/Botany/Horticulture 626, under the direction of Drs. P. Barak and E. Spalding, and was contributed to the Virtual Museum of Minerals and Molecules