Stable isotopomers of myo-inositol to uncover the complex MINPP1-dependent inositol phosphate network

Abstract

The water-soluble inositol phosphates (InsPs) represent a functionally diverse group of small-molecule messengers central to a myriad of cellular processes. However, we have an incomplete understanding of InsP metabolism because the available analytical toolset for inositol phosphates is rather limited. Here, we have synthesized and utilized fully and unsymmetrically 13C-labeled myo-inositol and inositol phosphates. These probes were applied in combination with nuclear magnetic resonance spectroscopy (NMR) and capillary electrophoresis mass spectrometry (CE-MS) to further annotate central aspects of InsP metabolism in human cells. The labeling strategy provided detailed structural information via NMR — down to individual enantiomers — which overcomes a crucial blind spot in the analysis of InsPs. We uncovered a novel branch of InsP dephosphorylation in human cells which is dependent on MINPP1, a phytase-like enzyme, that contributes to cellular homeostasis. Full characterization of MINPP1 activity in vitro and in cells, provided a clear picture of this multifunctional phosphatase. Metabolic labeling with stable isotopomers thus constitutes a powerful tool for investigating InsP networks in a variety of different biological contexts.

Regulations of myo-inositol homeostasis: Mechanisms, implications, and perspectives

“…This idea is supported by the observation that IP 6 and IP 2 are metabolically linked in multiple inositol polyphosphate phosphatase 1 (MINPP1) knockouts (Ucuncu et al, 2020). The very recent and thoughtful 13 C 6 -NMR analysis of MINPP1 activity revealed a distinctive IP 6 catabolism to IP 2 (Trung et al, 2022). Hence, an inositol phosphate cycle IP 2 to IP 6 and back to IP 2 would be only minimally influenced by fluctuations within the pool of inositol serving as an osmolyte.…”