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 myo-Ins(2,4,6)P3. The catalytic properties of the enzyme suggest a potential model for how the enzyme specifically recognizes its substrate Ca2+−InsP6 and produces myo-Ins(2,4,6)P3 from Ca2+−InsP6. These findings potentially provide evidence for a selective Ca2+−InsPs chelation between Ca2+ and two adjacent phosphate groups of inositol phosphates.