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.
Highlighting FeaturesShow all as ribbons. Beta strands are in magenta. Alpha helixes are cyan. The N-terminal lid is green. Show as strands with amino acids at active site Show as strands with basic amino acids at active site Show all as strands with amino acid residues histidine 59 and aspartate 339.
This crystal structure was obtained through x-ray diffraction of the crystallized enzyme and has a resolution of 2.5 Å.
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