Tools for analyzing the phosphoproteome and other phosphorylated biomolecules: a review

Enrichment, separation and mass spectrometric analysis of biomolecules carrying a phosphate group plays an important role in current analytical chemistry. Application areas range from the preparative enrichment of phospholipids for biotechnological purposes and the separation and purification of plasmid DNA or mRNA to the specific preconcentration of phosphoproteins and -peptides to facilitate their later identification and characterization by mass spectrometry. Most of the recent improvements in this field were triggered by the need for phosphopeptide enrichment technology for the analysis of cellular protein phosphorylation events with the help of liquid chromatography-mass spectrometry. The high sensitivity of mass spectrometry and the possibility to combine this technique with different separation modes in liquid chromatography have made it the method of choice for proteome analysis. However, in the case of phosphoprotein analysis, the low abundance of the resulting phosphopeptides and their low quality fragment spectra interfere with the identification of phosphorylation events. Recent developments in phosphopeptide enrichment and fragmentation technologies successfully helped to overcome these limitations. In this review, we will focus on sample preparation techniques in the field of phosphoproteomics, but also highlight recent advancements for the analysis of other phosphorylated biomolecules.