N-Terminal Labeling of Peptides by Trypsin-Catalyzed Ligation for Quantitative Proteomics

摘要

Labeling tryptic peptides with stable isotopes is one of the most important methods for quantitative proteomics, and many ingenious chemical labeling strategies have been developed. Incorporation of one isotopically labeled tag onto a peptide terminus represents an ideal labeling approach, as it would simplify the interpretation of mass spectra. Moreover, the absence of labels on the side chains would facilitate the quantification of post-translational modifications (PTMs). However, to date all the reported chemical labeling strategies, including dimethyl labeling, iTRAQ (iso-baric tags for absolute and relative quantification), and ICAT (isotope-coded affinity tags) result in the modification of side chains. One promising method to achieve the incorporation of a single tag is enzymatic labeling. Proteolytic ~(18)O labeling can specifically label tryptic peptide termini without modification of side chains, but the small change in mass and ~(18)O/~(16)O back-exchange, i.e. the exchange of ~(18)O with ~(16)O after the labeling process hinder its wide application in quantitative proteomics. Herein, we report a novel enzymatic labeling approach, in which trypsin is used as a ligase to specifically incorporate amino acids labeled with stable isotopes onto the N termini of peptides for quantitative analysis.