Mapping of phosphorylated proteins on two-dimensional polyacrylamide gels using protein phosphatase

This study developed an enzymatic method for high‐throughput mapping of phosphoproteins on two‐dimensional (2‐D) polyacrylamide gels. Proteins of cultured rat skin fibroblasts were divided into two aliquots, one of which was dephosphorylated using recombinant lambda protein phosphatase and the other was not treated with the enzyme. The two aliquots were then subjected to 2‐D electrophoresis. Phosphoproteins could be mapped on the 2‐D gel of the nontreated aliquot by comparing the gels of the two aliquots, because the phosphoproteins in the treated aliquot shifted to more basic positions on the gel. This technique revealed that approximately 5% of the detectable proteins were phosphorylated. Fourteen phosphoproteins were identified by mass spectrometry, including proteasome component C8 and small glutamine‐rich tetratricopeptide repeat‐containing protein. Furthermore, the extent of phosphorylation of two actin modulating proteins, destrin and cofilin, was found to be significantly reduced when the cells were chemically or enzymatically detached from the culture dishes. The method developed by this study can generally be applied to all biological materials and is useful for high‐throughput mapping of phosphoproteins in proteome research.