Proteome-wide analysis of protein carboxy termini: C terminomics.

As proteome-wide C-terminal sequence analysis has been largely intractable, we developed a polymer-based enrichment approach to profile protein C-terminal peptides by mass spectrometry and identified hundreds of C-terminal peptides in the Escherichia coli proteome. We isotopically labeled GluC protease-digested and undigested samples and identified GluC substrates and their cleavage sites by quantification of neo-C-terminal peptides. Our method thus enables global annotation of protein C-terminal posttranslational modifications, including proteolytic truncations.