Phosphoproteomic identification and functional characterization of protein kinase substrates by 2D-DIGE and Phos-tag PAGE.

Protein phosphorylation is one of the most common post-translational modifications in eukaryotes and can regulate diverse properties of proteins. Protein kinases are encoded by more than 500 genes in higher eukaryotes and play central roles in various cellular signaling pathways. Consequently, genetic abnormalities of protein kinases have been implicated in many diseases. To fully understand the complex phosphorylation-mediated signaling networks, it is important to globally identify and functionally characterize in vivo substrates of individual protein kinases. Advances in electrophoresis-based phosphoproteomic technologies such as two-dimensional difference gel electrophoresis (2D-DIGE) following immobilized metal affinity chromatography (IMAC) and phosphate-affinity Phos-tag PAGE have enabled efficient and detailed analysis of protein kinase substrates. Here, we describe physiological functions of the newly identified substrates of several disease-related protein kinases including ERK, PKD and PINK1.