β-Propeller Phytase Hydrolyzes Insoluble Ca2+-Phytate Salts and Completely Abrogates the Ability of Phytate To Chelate Metal Ions

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• 作者：Ok-Hee Kim ; Young-Ok Kim ; Jae-Hoon Shim ; Yun-Shin Jung ; Woo-Jin Jung ; Won-Chan Choi ; Heeseob Lee ; Sang-Jun Lee ; Kyung-Kil Kim ; Joong-Huck Auh ; Hyeonjin Kim ; Jung-Wan Kim ; Tae-Kwang Oh ; Byung-Chul Oh
• 刊名：Biochemistry
• 出版年：2010
• 出版时间：November 30, 2010
• 年：2010
• 卷：49
• 期：47
• 页码：10216-10227
• 全文大小：1227K
• 年卷期：v.49,no.47(November 30, 2010)
• ISSN：1520-4995

文摘

Phytate is an antinutritional factor that influences the bioavailability of essential minerals by forming complexes with them and converting them into insoluble salts. To further our understanding of the chemistry of phytate’s binding interactions with biologically important metal cations, we determined the stoichiometry, affinity, and thermodynamics of these interactions by isothermal titration calorimetry. The results suggest that phytate has multiple Ca²⁺-binding sites and forms insoluble tricalcium- or tetracalcium-phytate salts over a wide pH range (pH 3.0−9.0). We overexpressed the β-propeller phytase from Hahella chejuensis (HcBPP) that hydrolyzes insoluble Ca²⁺-phytate salts. Structure-based sequence alignments indicated that the active site of HcBPP may contain multiple calcium-binding sites that provide a favorable electrostatic environment for the binding of Ca²⁺-phytate salts. Biochemical and kinetic studies further confirmed that HcBPP preferentially recognizes its substrate and selectively hydrolyzes insoluble Ca²⁺-phytate salts at three phosphate group sites, yielding the final product, myo-inositol 2,4,6-trisphosphate. More importantly, ITC analysis of this final product with several cations revealed that HcBPP efficiently eliminates the ability of phytate to chelate several divalent cations strongly and thereby provides free minerals and phosphate ions as nutrients for the growth of bacteria. Collectively, our results provide significant new insights into the potential application of HcBPP in enhancing the bioavailability and absorption of divalent cations.