Synthesis and nonradioactive micro-analysis of diphosphoinositol phosphates by HPLC with postcolumn complexometry

Area of Science:

• Biochemistry
• Analytical Chemistry
• Cell Biology

Background:

• Inositol phosphates, including inositol hexakisphosphate (InsP(6)), play crucial roles in cellular signaling.
• Separating and identifying various phosphorylated inositol species, particularly pyrophosphorylated forms like diphosphoinositol pentakisphosphate (PPInsP(5)) and bis-diphosphoinositol tetrakisphosphate (bisPPInsP(4)), is challenging due to their structural complexity and low abundance.
• Existing methods often rely on radioactivity, limiting their application in routine cellular studies.

Purpose of the Study:

• To develop a nonradioactive, high-performance anion-exchange chromatographic (HPAEC) method for the separation of InsP(6) and its pyrophosphorylated isomers.
• To generate reference standards for bisPPInsP(4) isomers using a novel nonenzymatic synthesis approach.
• To apply the developed method for identifying bisPPInsP(4) isomers in mammalian cells.

Main Methods:

• High-performance anion-exchange chromatography (HPAEC) with acidic elution for separating inositol phosphates.
• Nonenzymatic shotgun synthesis of InsP(6) using creatine phosphate and anion-exchange beads to generate bisPPInsP(4) reference standards.
• Characterization of synthesized isomers by comparison with known compounds and limited hydrolysis.

Main Results:

• The HPAEC method successfully resolved four separable PPInsP(5) isomers into three peaks and nine separable bisPPInsP(4) isomers into nine distinct peaks.
• The entire separation procedure was optimized to be completed within 20-36 minutes.
• Nonenzymatic synthesis yielded a mixture containing PPInsP(5), bisPPInsP(4), and trisPPInsP(3) isomers, from which bisPPInsP(4) standards were isolated.
• The method allowed for the identification of the major bisPPInsP(4) isomer in mammalian cells without requiring material for NMR analysis.

Conclusions:

• A robust, nonradioactive HPAEC method has been established for the efficient separation and analysis of InsP(6) and its pyrophosphorylated derivatives.
• The nonenzymatic synthesis provides a valuable source of reference standards for bisPPInsP(4) isomers.
• This analytical technique significantly advances the study of inositol phosphate metabolism in cellular systems, enabling isomer identification without extensive sample preparation or specialized equipment.