Crystal structures of Bacillus alkaline phytase in complex with divalent metal ions and inositol hexasulfate |
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Authors: | Zeng Yi-Fang Ko Tzu-Ping Lai Hui-Lin Cheng Ya-Shan Wu Tzu-Hui Ma Yanhe Chen Chun-Chi Yang Chii-Shen Cheng Kuo-Joan Huang Chun-Hsiang Guo Rey-Ting Liu Je-Ruei |
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Affiliation: | 1 Institute of Biotechnology, National Taiwan University, Taipei 106, Taiwan2 Department of Animal Science and Technology, National Taiwan University, Taipei 106, Taiwan3 Institute of Microbiology and Biochemistry, National Taiwan University, Taipei 106, Taiwan4 Institute of Biological Chemistry, Academia Sinica, Taipei 115, Taiwan5 Institute of Biomedical Science, Academia Sinica, Taipei 115, Taiwan6 Agricultural Biotechnology Research Center, Academia Sinica, Taipei 115, Taiwan7 Genozyme biotechnology Inc., Taipei 106, Taiwan8 Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin 300308, China |
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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. |
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Keywords: | HAP, histidine acid phosphatase PTP, protein tyrosine phosphatase HAP, histidine acid phosphatase PAP, purple acid phosphatase BPP, β-propeller phytase IHS, myo-inositol hexasulfate |
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