title: Crystal structure of a heat-resilient phytase from Aspergillus fumigatus, carrying a phosphorylated histidine.
abstract: In order to understand the structural basis for the high thermostability of phytase from Aspergillus fumigatus, its crystal structure was determined at 1.5 A resolution. The overall fold resembles the structure of other phytase enzymes. Aspergillus niger phytase shares 66% sequence identity, however, it is much less heat-resistant. A superimposition of these two structures reveals some significant differences. In particular, substitutions with polar residues appear to remove repulsive ion pair interactions and instead form hydrogen bond interactions, which stabilize the enzyme; the formation of a C-terminal helical capping, induced by arginine residue substitutions also appears to be critical for the enzyme's ability to refold to its active form after denaturation at high temperature. The heat-resilient property of A.fumigatus phytase could be due to the improved stability of regions that are critical for the refolding of the protein; and a heat-resistant A.niger phytase may be achieved by mutating certain critical residues with the equivalent residues in A.fumigatus phytase. Six predicted N-glycosylation sites were observed to be glycosylated from the experimental electron density. Furthermore, the enzyme's catalytic residue His59 was found to be partly phosphorylated and thus showed a reaction intermediate, providing structural insight, which may help understand the catalytic mechanism of the acid phosphatase family. The trap of this catalytic intermediate confirms the two-step catalytic mechanism of the acid histidine phosphatase family.
authors.affiliation: Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Tao
authors.initials: T
authors.lastname: Xiang
authors.forename: Qun
authors.initials: Q
authors.lastname: Liu
authors.forename: Ashley M
authors.initials: AM
authors.lastname: Deacon
authors.forename: Matthew
authors.initials: M
authors.lastname: Koshy
authors.forename: Irina A
authors.initials: IA
authors.lastname: Kriksunov
authors.forename: Xin Gen
authors.initials: XG
authors.lastname: Lei
authors.forename: Quan
authors.initials: Q
authors.lastname: Hao
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Thiel
mesh_terms: D010832:6-Phytase / Q000737:chemistry* / Q000378:metabolism; D000595:Amino Acid Sequence; D001232:Aspergillus fumigatus / Q000201:enzymology*; D001665:Binding Sites; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D004795:Enzyme Stability; D006031:Glycosylation; D006639:Histidine / Q000737:chemistry*; D006358:Hot Temperature; D006860:Hydrogen Bonding; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid
chemical_list: D006639:Histidine; D010832:6-Phytase