Myo-inositol hexakisphosphate is the most abundant organic phosphate molecule in the terrestrial environment, and arises predominantly, we assume, from the degradation of plants in which this molecule accumulates in storage tissues. Nature, however, always ‘puts molecules to use’ in many different ways. Bacterial pathogens such as Vibrio cholerae exploit host, eukaryote, inositol hexakisphosphate to activate RTX (repeats in toxin) protein to disrupt the host cell cytoskeleton. In yeast, inositol hexakisphosphate contributes to mRNA export from the nucleus. In zebra fish, ablation of ipk1, the gene which encodes the enzyme that catalyzes inositol hexakisphosphate synthesis, disrupts left-right organ asymmetry; while knockdown of the expression of ipk1 disrupts the ciliary beating rhythm of Kupffer’s vesicle, an organ with important roles in organ positioning. The cestode parasite Echinococcus granulosus forms hydatid cysts in its animal hosts. The laminal layer of these cysts is composed of a glycoprotein matrix with semicrystalline deposits of inositol hexakisphosphate. It is likely that in all these examples inositol hexakisphosphate synthesis is catalysed by orthologues of the Arabidopsis enzyme Ipk1. The crystal structure of this enzyme, recently solved by Beatriz Gonzalez’ group, CISC, Madrid, reveals how, uniquely among inositol phosphate kinases, this enzyme phosphorylates the axial 2-OH of myo-inositol 1,3,4,5,6-pentakisphosphate to produce myo-inositol hexakisphosphate.

Below: The active site of AtIpk1 showing inositol hexakisphosphate and ADP products of catalysis.