Protein pyrophosphorylation by diphosphoinositol pentakisphosphate (InsP7).

Diphosphoinositol polyphosphates, also known as inositol pyrophosphates, are a family of water soluble inositol phosphates that possess diphosphate or pyrophosphate moieties. In the presence of divalent cations such as Mg(2+), the "high energy" beta phosphate can be transferred from the inositol pyrophosphates, InsP(7) and InsP(8), to prephosphorylated serine residues on proteins, to form pyrophosphoserine. This chapter provides detailed methods to identify proteins that are substrates for pyrophosphorylation by InsP(7), conduct phosphorylation assays on purified protein, and detect protein pyrophosphorylation.