A synthetic diphosphoinositol phosphate analogue of inositol trisphosphate†

Abstract

We describe the synthesis and biological evaluation of 1-PP-Ins(4,5)P ₂, the first diphosphate-containing analogue of the intracellular signalling molecule Ins(1,4,5)P ₃.

Abstract

Diphosphoinositol phosphates (PP-InsPs) are inositol phosphates (InsPs) that contain PP (diphosphate) groups. Converting a phosphate group in an InsP into a diphosphate has been reported to enhance affinity for some binding proteins. We synthesised 1-PP-Ins(4,5)P ₂, the first diphosphate analogue of the intracellular signalling molecule InsP ₃, and examined its effects on InsP ₃ receptors, which are intracellular Ca ²⁺ channels. 1-PP-Ins(4,5)P ₂ was indistinguishable from InsP ₃ in its ability to bind to and activate type 1 InsP ₃ receptors, indicating that the diphosphate modification of InsP ₃ affected neither affinity nor efficacy. Nevertheless, 1-PP-Ins(4,5)P ₂ is the most potent 1-phosphate modified analogue of InsP ₃ yet identified. PP-InsPs are generally hydrolysed by diphosphoinositol polyphosphate phosphohydrolases (DIPPs), but 1-PP-Ins(4,5)P ₂ was not readily metabolised by human DIPPs. Differential scanning fluorimetry showed that 1-PP-Ins(4,5)P ₂ stabilises DIPP proteins, but to a lesser extent than naturally occurring substrates 1-PP-InsP ₅ and 5-PP-InsP ₅. The non-hydrolysable InsP ₇ analogues 1-PCP-InsP ₅ and 5-PCP-InsP ₅ showed comparable stabilising abilities to their natural counterparts and may therefore be promising substrate analogues for co-crystallisation with DIPPs.

Notes

†Electronic supplementary information (ESI) available: NMR spectra, additional DSF data and details of molecular docking experiments. See DOI: 10.1039/c8md00149a