Can mass spectrometry be used to identify sites of post-translational modifications (PTMs)?
The identification of peptides and proteins is done by matching the experimentally acquired mass spec peptide fragment information to the theoretical peptide values obtained from an in-silico tryptic digestion of a protein database. Identification of PTMs can therefore be done post-MS acquisition by selecting the modifications of interest as variables to be queried during the identification of peptides by the database search engine. Alternatively, peptides carrying certain modifications such as glycosylation, phosphorylation, sulfation, acetylation, etc. can be selectively targeted for analysis by the use specific mass spec methods such as precursor ion scans, neutral loss scans and multiple reaction monitoring scans. For some post-translational modifications, such as phosphorylation, an important limitation for the identification of modified peptides is their low abundance. For this reason, it is generally a good idea to enrich the modified protein and/or the peptides using an appropr