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-Ca 2+ -P) formed between Ca 2+ and two adjacent phosphate groups of its natural substrate phytate (InsP 6 ). The specific recognition of a bidentate chelation enables the enzyme to sequentially hydrolyze one of the phosphate groups in a bidentate of Ca 2+ -InsP 6 to yield a myo-inositol trisphosphate (InsP 3 ) and three phosphates as the final products. A comparative analysis of 1 H- and 13 C NMR spectroscopy with the aid of 2D NMR confirms that the chemical structure of the final product is myo-Ins(2,4,6)P 3 . The catalytic properties of the enzyme suggest a potential model for how the enzyme specifically recognizes its substrate Ca 2+ -InsP 6 and produces myo-Ins(2,4,6)-P 3 from Ca 2+ -InsP 6 . These findings potentially provide evidence for a selective Ca 2+ -InsPs chelation between Ca 2+ and two adjacent phosphate groups of inositol phosphates.