HEK293T cells expressing SRC kinase domain variants fused with N-terminal GFP domain. Cells expressing only GFP were used as control. Cell lysate were trypsinized, collected in 1.5 mL tubes, and prepared for mass spectrometry (MS) analysis. Protein digestion, tryptic peptide purification, and phosphopeptide enrichment were performed using the EasyPep™ Mini MS Sample Prep Kit (A40006) and the High-Select™ TiO₂ Phosphopeptide Enrichment Kit (A32993) from Thermo Scientific according to the manufacturer’s instructions.