Simultaneous Adsorption of Intact Glycoproteins and Phosphoproteins Using Hydrophilic Titanium (IV) Ion-Immobilized Cotton Fiber Functionalized by Phytic Acid Assembly

Protein glycosylation and phosphorylation are two important post-translational modifications and play significant roles in various biological processes. However, both glycoproteins and phosphoproteins are in low abundance in complex samples, which hinders their characterization. In this work, we developed a novel method for the simultaneous adsorption of glycoproteins and phosphoproteins based on solid phase extraction. By virtue of the unique structure of hydrophilic titanium (IV) ion immobilized cotton fiber functionalized with phytic acid (denoted as Ti4+-PA-cotton), glycoproteins, and phosphoproteins could be efficiently enriched in one-step incubation and eluted in sequence. The newly prepared Ti4+-PA-cotton was well characterized, and the adsorption isotherms and kinetics were studied. The maximum adsorption capacities of Ti4+-PA-cotton for β-casein and HRP were 833.3 mg/g and 384.6 mg/g with the adsorption rate of 259.1 and 63.1 mg/g·min. Standard protein mixture of BSA, HRP, and β-casein was used to test the enrichment ability as a proof of concept. The SDS-PAGE results demonstrated that Ti4+-PA-cotton had an excellent enrichment performance and possessed an outstanding application potential in the analysis of glycoproteins and phosphoproteins.