Reagents for Isobaric Labeling Peptides in Quantitative Proteomics.

Currently, the commercial reagents for isobaric peptides labeling (TMT and iTRAQ) have some drawbacks, such as high cost in experiments, especially in quantitation for the modified peptides, and inconvenient handling for variable sizes of samples. Herein, we developed a set of 10-plex isobaric tags (IBT) with high stability and low cost. The labeled peptides were sensitively detected on Orbitrap Q Exactive MS with an MS2 resolution of 35 000 at 30% NCE, while the peptides were efficiently labeled over 97% by IBT at a ratio of 10:1 of reagent/peptide (w/w) in 200 mM TEAB buffer for 2 h. The IBT labeling was demonstrated with a wide dynamic range of 50-fold without obvious matrix effects on quantification. Importantly, there was little quantification bias found among the individual IBT tags, indicating that the peptides labeled by different tags were quantitatively comparable. The IBT 10-plex reagents were applied for dynamically monitoring the quantitative responses of phosphoproteome stimulated by EGF treatment in HeLa cells. In total, 5 361 unique phosphopeptides were identified, which reached a similar conclusion as others reported. The IBT reagents were therefore experimentally proven as a new type of reagents for isobaric peptides labeling and useful in a large quantity peptides of quantitative proteomics.