title: Crystal structures of Bacillus alkaline phytase in complex with divalent metal ions and inositol hexasulfate.
abstract: Alkaline phytases from Bacillus species, which hydrolyze phytate to less phosphorylated myo-inositols and inorganic phosphate, have great potential as additives to animal feed. The thermostability and neutral optimum pH of Bacillus phytase are attributed largely to the presence of calcium ions. Nonetheless, no report has demonstrated directly how the metal ions coordinate phytase and its substrate to facilitate the catalytic reaction. In this study, the interactions between a phytate analog (myo-inositol hexasulfate) and divalent metal ions in Bacillus subtilis phytase were revealed by the crystal structure at 1.25 Å resolution. We found all, except the first, sulfates on the substrate analog have direct or indirect interactions with amino acid residues in the enzyme active site. The structures also unraveled two active site-associated metal ions that were not explored in earlier studies. Significantly, one metal ion could be crucial to substrate binding. In addition, binding of the fourth sulfate of the substrate analog to the active site appears to be stronger than that of the others. These results indicate that alkaline phytase starts by cleaving the fourth phosphate, instead of the third or the sixth that were proposed earlier. Our high-resolution, structural representation of Bacillus phytase in complex with a substrate analog and divalent metal ions provides new insight into the catalytic mechanism of alkaline phytases in general.
authors.affiliation: Institute of Biotechnology, National Taiwan University, Taipei 106, Taiwan.
authors.forename: Yi-Fang
authors.initials: YF
authors.lastname: Zeng
authors.forename: Tzu-Ping
authors.initials: TP
authors.lastname: Ko
authors.forename: Hui-Lin
authors.initials: HL
authors.lastname: Lai
authors.forename: Ya-Shan
authors.initials: YS
authors.lastname: Cheng
authors.forename: Tzu-Hui
authors.initials: TH
authors.lastname: Wu
authors.forename: Yanhe
authors.initials: Y
authors.lastname: Ma
authors.forename: Chun-Chi
authors.initials: CC
authors.lastname: Chen
authors.forename: Chii-Shen
authors.initials: CS
authors.lastname: Yang
authors.forename: Kuo-Joan
authors.initials: KJ
authors.lastname: Cheng
authors.forename: Chun-Hsiang
authors.initials: CH
authors.lastname: Huang
authors.forename: Rey-Ting
authors.initials: RT
authors.lastname: Guo
authors.forename: Je-Ruei
authors.initials: JR
authors.lastname: Liu
mesh_terms: D010832:6-Phytase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001412:Bacillus subtilis / Q000201:enzymology*; D002384:Catalysis; D002413:Cations, Divalent / Q000378:metabolism*; D018360:Crystallography, X-Ray; D007294:Inositol / Q000031:analogs & derivatives* / Q000378:metabolism; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D055503:Protein Multimerization; D013379:Substrate Specificity
chemical_list: D002413:Cations, Divalent; C013063:inositol hexasulfate; D007294:Inositol; D010832:6-Phytase