Phosphopeptides were enriched using High-Select™ TiO2 Phosphopeptide Enrichment Kits (Thermo Fisher Scientific, catalog A32993). After preparing spin tips as per manufacturer’s instructions, approximately 2 mg of labeled and mixed peptides were repeatedly applied to 3 separate TiO2 spin tips and eluted in 50 μL elution buffer. Elutions were combined for phosphoproteomics. The flow through from each tip was saved and combined for global proteomics.
