Purified QPCTL was incubated with the SHP2 (aa 17-35) peptide, and the modification of SHP2 (aa 17-35) was analyzed by nano-electrospray ionization mass spectrometry (nanoESI-MS). The modification of SHP2 (aa 17-35) alone (without co-incubation with purified QPCTL protein) was monitored by nanoelectrospray ionization mass spectrometry (nanoESI-MS).