Profiling Protein Tyrosine Phosphatase Specificity with SAMDI Mass Spectrometry and Peptide Arrays

The opposing activities of phosphatases and kinases determine the phosphorylation status of proteins, yet kinases have received disproportionate attention in studies of cellular processes, with the roles of phosphatases remaining less understood. This Research Article describes the use of phosphotyrosine-containing peptide arrays together with matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to directly profile phosphatase substrate selectivities. Twenty-two protein tyrosine phosphatases were characterized with the arrays to give a profile of their specificities. An analysis of the data revealed that certain residues in the substrates had a conserved effect on activity for all enzymes tested, including the general rule that inclusion of a basic lysine or arginine residue on either side of the phosphotyrosine decreased activity. This insight also provides a new perspective on the role of a R1152Q mutant in the insulin receptor, which is known to exhibit a lower phosphorylation level an...