Over the years we have developed a large number of methods for enrichment of post-translational modified (PTM) peptides, from complex biological matrices, in order to make it possible to study these in nature. A PTM is the attachment of a chemical group to a protein after or during protein synthesis and the global analysis of PTMs is termed PTMomics. Many PTMs are reversible and numerous enzymes for their controlled attachment and removal exist. In fact, about 5% of proteome in an eukaryote cell are enzymes capable of add or remove PTMs. Often a complex interplay between these enzymes modulates the PTM level of a protein to fine-tune the protein activity, function and interaction, allowing a level of delicate control of signaling pathways not possible in any other way. Characterization of the PTMome requires specialized and sensitive strategies aiming not only at monitoring one single PTM but rather a repertoire of PTMs in order to obtain a larger picture of the signaling pathways.
Here we will discuss strategies for large scale PTMomics and show an example of one of the workflows we have developed for assessment of phosphorylated peptides, sialylated glycopeptides, lysine acetylated peptides and free and reversibly modified cysteine-containing peptides from the same sample. We will illustrated the workflow by showing the characterization of short time T-cell signaling and ultra-short time stimulation of isolated nerve terminals.