Dissecting inositol pyrophosphates signalling

My research is focused on the study of inositol phosphates, a large family of small molecules that regulate many essential and basic functions in all living organisms, including heart muscle contraction, the release of neurotransmitters in the brain, mammalian cell survival and the migration of cells of the immune system. Two new members of this family (called IP7 and IP8) have the exceptionally unusual property of containing high energy Pyro-phosphate bonds. This is similar to the high energy phosphate bond found in ATP, the main energy storage molecule found in all cells. Like ATP, IP7 and IP8 are also found in all cells analyzed so far, ranging from fungi to humans, but very little is known about their physiological functions. The release of energy from their high energy bonds could, potentially, drive a variety of fundamental biochemical processes and the goal of my research is to identify the physiological role of this novel and exciting class of high-energy molecules.

Inositol phosphates (IP) occur ubiquitously in biological tissues. The most widely studied IP is inositol 1,4,5-trisphosphate (IP3), the second messenger that triggers calcium release from intracellular stores. Interestingly, the six carbons that comprise the fully phosphorylated inositol ring of IP6 (Inositol hexakisphosphate, also known as phytic acid) can be further phosphorylated, creating more polar inositol polyphosphates. These higher inositol phosphates contain one, two or more high-energy Pyro-phosphate bonds, similar to the high-energy bonds present in ATP. The best-characterized inositol pyrophosphates are the diphosphoinositol pentakisphosphate (IP7) and the bis-diphosphoinositol tetrakisphosphate (IP8). In cells the IP6 concentration is very stable, while IP7 and IP8 are metabolized at a very high rate. Every hour, 20 to 50% of the large IP6 reservoir cycles through inositol pyrophosphates, and it has been suggested that this cycle represent a molecular switch activity that regulates intracellular signalling.||Our ability to produce radiolabeled IP7 with high specific activity has allowed us to detect the direct transfer of the radiolabel beta phosphate from IP7 to proteins. This phosphorylation mechanism defines a yet new kind of protein post-translational modification. A recent study has shown that inositol pyrophosphates donate the phosphate group to pre-phosphorylated serines, thus generating a pyro-phosphorylated protein. Although we are able to reproducibly transfer phosphate moieties from IP7 to pre-phosphorylated serine of proteins in vitro and have indirect evidence that IP7 can directly mediate phosphorylation in vivo, the molecular mechanisms underlying IP7-dependent protein pyro-phosphorylation in vivo and the physiological consequence of such, are not fully elucidated yet. The main objective of my laboratory is to identify the physiological functions of inositol pyro-phosphates. We are employing several experimental models from yeast Saccharomyces cerevisiae, a simple but powerful genetic model, to mouse knockout to mimic human physiology. We are routinely using several biochemical, molecular biology and cell biology techniques.||It has become increasingly clear that inositol pyrophosphates have a very basic signalling function inside all eukaryotic cells. It is likely that the inositol pyro-phosphates have evolved dedicated roles due to their unique biochemistry. The potential therapeutic potential of such research is supported by the recent identification of the critical role inositol pyrophosphates in the regulation of insulin secretion and oncogenic processes. We have substantially contributed to both studies.