Phosphatidylinositol phosphate kinases

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Phosphatidylinositol phosphate kinases (PIPK) are kinases that phosphorylate the phosphoinositides PtdInsP and PtdInsP₂ that are derivatives of phosphatidylinositol (PtdIns). It has been found that PtdIns is only phosphorylated on three (3,4,5) of its five hydroxyl groups, possibly because D-2 and D-6 hydroxyl groups cannot be phosphorylated because of steric hindrance ^[1]. All 7 combinations of phosphorylated PtdIns have been found in animals, all except PtdIns(3,4,5)P₃ have been found in plants ^[2].

PIPKs are today divided into three groups, type I, II and III that share significant sequence homology but differ in the substrate specificities, subcellular localisations and functions.^[3] Type 1 are PIPKs that phosphorylate PtdIns4P to PtdIns(4,5)P₂ and are called PtdIns4P 5-kinases because they phosphorylate on the D-5 hydroxyl group. Type II PIPKs phosphorylate PtdIns5P at the D-4 site and are called PtdIns5P 4-kinases. And finally PIPKs of type III are PtdIns3P 5-kinases that phosphorylate PtdIns to PtdIns(3,5)P₂, which prototype is Fab1 in yeast.

[edit] References

1. ^ Pettitt TR, Dove SK, Lubben A, Calaminus SDJ, Wakelam MJO. Analysis of intact phosphoinositides in biological samples. American Soc f Biochem and Mol Biol 2006; 47:1588-1596
2. ^ Muller-Roeber B, Pical C. Inositol Phospholipid Metabolism in Arabidopsis. Characterized and Putative Isoforms of Inositol Phospholipid Kinase and Phosphoinositide-Specific Phospholipase C. Plant Physiol 2002 130:22–46
3. ^ Anderson RA, Boronenkov IV, Doughman SD, Kunz J, Loijens JC . Phosphatidylinositol phosphate kinases, a multifaceted family of signalling enzymes. J Biol Chem 1999; 274:9907-9910