Diphosphoinositol Pentakisphosphate Kinase 1 (PPIP5K1)

Inositol phosphates (IPs) and diphosphoinositol phosphates (PP-IPs), also known as inositol pyrophosphates, act as cell signaling molecules. HISPPD2A has both IP6 kinase and PP-IP5 (also called IP7) kinase activities that produce the high-energy pyrophosphates PP-IP5 and PP2-IP4 (also called IP8), respectively.

IP6K phosphorylates IP6 to produce IP7 with the pyrophosphate at position 5 of the inositol ring. The yeast homolog, Vip1, produced different IP7 products, with pyrophosphates at positions 4 or 6. Both yeast and human proteins could generate IP8 containing 2 pyrophosphates. Mutation analysis showed that the ATP-grasp domain of yeast Vip1 was sufficient for IP6 kinase activity.