Final Report Summary - EUROPOLYPS (Identity and functions of polyphosphate polymerases in eukaryotes)
Phosphorus is an essential nutrient for all organisms, important to synthesize our genetic information and the membranes surrounding our cells. Phosphorus also forms an important energy currency and signaling molecule. Phosphorus is taken up by cells in the form of inorganic phosphate. While our diet contains sufficient amounts of phosphate, microorganisms and plants have to take up phosphate from the soil where it is scarcely available. Thus microorganisms and plants have evolved sophisticated ways to sense, uptake, transport and store phosphate. One such storage form is inorganic polyphosphate, a long linear polymer of many phosphate units. In the frame of the ERC grant EUROPolyPs we have uncovered how cells sense phosphate levels to decide whether to store or transport it. Under conditions where there is sufficient phosphate, a signaling molecule called inositol pyrophosphate accumulates in cells. The signaling molecule is bound by a protein sensor domain, which in turn regulates to activity of enzymes, transporters and transcription factors involved in phosphate storage, transport or signaling. Under phosphate starvation, the levels of inositol pyrophosphates drop, the sensor domain is not in contact with its signal any longer and thereby instructs proteins to alter their activity. Importantly, this novel phosphate sensing and signaling mechanism is conserved among different higher organisms including fungi, plants and animals.