Nano-titanium dioxide composites for the enrichment of phosphopeptides

Abstract

Protein phosphorylation is one of the most important known posttranslational modifications and the strategy to enrich phosphopeptides becomes a critical issue for mapping protein phosphorylation sites. In this study, nano-titanium dioxide (TiO 2) composites were synthesized, characterized, and demonstrated to have high loading capacity and high capture efficiency for enriching phosphopeptides. TiO 2 nanoparticles were first silanized with methacryloxypropyltrimethoxysilane (MPTMS) and then were photopolymerized in the presence of a diacrylate crosslinker. The chemical bonds formed by the reaction were confirmed by both FT-IR and X-ray photoelectron spectroscopy (XPS). Scanning electron microscopy (SEM) further reveals that agglomeration of the particles was created by the crosslinking, which allowed the nanocomposites to be well retained within the cartridge and used as the chromatographic packing material. Titration with phenyl phosphate indicated that the TiO 2 nanocomposites have two times as much phosphate binding capacity compared with 5 μm TiO 2 particles. Moreover, based on repetitive analyses of the tryptic digest deduced from pure proteins as well as from protein mixtures containing phospho and non-phospho proteins, the capture efficiency of TiO 2 nanocomposites was determined to be two to five times larger compared with 5 μm TiO 2 particles. The cost for preparing nanocomposite TiO 2 is low and it holds great promises to be used as chromatographic materials for phosphopeptide enrichment.