Probing the phosphoproteome of HeLa cells using nanocast metal oxide microspheres for phosphopeptide enrichment.

Metal oxide affinity chromatography (MOAC) has become a prominent method to enrich phosphopeptides prior to their analysis by liquid chromatography-mass spectrometry. To overcome limitations in material design, we have previously reported the use of nanocasting as a means to generate metal oxide spheres with tailored properties. Here, we report on the application of two oxides, tin dioxide (stannia) and titanium dioxide (titania), for the analysis of the HeLa phosphoproteome. In combination with nanoflow LC-MS/MS analysis on a linear ion trap-Fourier transform ion cyclotron resonance instrument, we identified 619 phosphopeptides using the new stannia material, and 896 phosphopeptides using titania prepared in house. We also compared the newly developed materials to commercial titania material using an established enrichment protocol. Both titania materials yielded a comparable total number of phosphopeptides, but the overlap of the two data sets was less than one-third. Although fewer peptides were identified using stannia, the complementarity of SnO(2)-based MOAC could be shown as more than 140 phosphopeptides were exclusively identified by this material.