Displacers improve the selectivity of phosphopeptide enrichment by metal oxide affinity chromatography

Background A key process in cell regulation is protein phosphorylation, which is catalyzed by protein kinases and phosphatases. However, phosphoproteomics studies are difficult because of the complexity of protein phosphorylation and the number of phosphorylation sites. Methods We describe an efficient approach analyzing phosphopeptides in single, separated protein by two-dimensional gel electrophoresis. In this method, a titanium oxide (TiO2)-packed NuTip is used as a phosphopeptide trap, together with displacers as lactic acid in the loading buffer to increase the efficiency of the interaction between TiO2 and phosphorylated peptides. Results The results were obtained from the comparison of mass spectra of proteolytic peptides of proteins with a matrix-assisted laser desorption-ionization-time of flight (MALDI-TOF) instrument. Conclusions This method has been applied to identifying phosphoproteins involved in the symbiosis Rhizobium etli-Phaseolus vulgaris.