Development of immobilized Sn4+ affinity chromatography material for highly selective enrichment of phosphopeptides

In this work, we first immobilized tin(IV) ion on polydopamine-coated magnetic graphene (magG@PDA) to synthesize Sn4+-immobilized magG@PDA (magG@PDA-Sn4+) and successfully applied the material to highly selective enrichment of phosphopeptides. The material gathered the advantages of large surface area of graphene, superparamagnetism of Fe3O4, good hydrophilicity and biocompatibility of polydopamine, and strong interaction between Sn4+ and phosphopeptides. The enrichment performance of magG@PDA-Sn4+ toward phosphopeptides from digested -casein at different concentrations, with and without added digested BSA was investigated and compared with magG@PDA-Ti4+. The results showed high selectivity and sensitivity of the Sn4+-IMAC material toward phosphopeptides, as good as the Ti4+-IMAC material. Finally, magG@PDA-Sn4+ was applied to the analysis of endogenous phosphopeptides from a real sample, human saliva, with both MALDI-TOF MS and nano-LC-ESI-MS/MS. The results indicated that the as-synthesized Sn4+-IMAC material not only has good enrichment performance, but also could serve as a supplement to the Ti4+-IMAC material and expand the phosphopeptide coverage enriched by the single Ti4+-IMAC material, demonstrating the broad application prospects of magG@PDA-Sn4+ in phosphoproteome research.