Ca²⁺-inositol phosphate chelation mediates the substrate specificity of β-propeller phytase

Inositol phosphates are recognized as having diverse and critical roles in biological systems. In this report, kinetic studies and TLC analysis indicate that β-propeller phytase is a special class of inositol phosphatase that preferentially recognizes a bidentate (P-Ca²⁺-P) formed between Ca²⁺ and two adjacent phosphate groups of its natural substrate phytate (InsP₆). The specific recognition of a bidentate chelation enables the enzyme to sequentially hydrolyze one of the phosphate groups in a bidentate of Ca²⁺-InsP₆ to yield a myo-inositol trisphosphate (InsP₃) and three phosphates as the final products. A comparative analysis of ¹H- and ¹³C NMR spectroscopy with the aid of 2D NMR confirms that the chemical structure of the final product is wyo-Ins(2,4,6)P₃. The catalytic properties of the enzyme suggest a potential model for how the enzyme specifically recognizes its substrate Ca ²⁺-InsP₆ and produces myo-Ins(2,4,6)-P₃ from Ca²⁺-InsP₆- These findings potentially provide evidence for a selective Ca²⁺-InsP₆ chelation between Ca ²⁺ and two adjacent phosphate groups of inositol phosphates.