Recent advances in the field of protein post-translational modifications (PTMs) have uncovered their widespread occurrence and physiological relevance. However, for comprehensive analysis of PTMs specific

peptide enrichment approaches and dedicated analyses are required, without which PTMs are usually undersampled and overlooked, respectively. In the absence of functional annotation of proteins from PTMs many key functions of bioactive proteins will be opaque and hence hypotheses based on traditional shotgun analyses, may be misleading or even worse, totally wrong. PTM of proteins constitutes a highly diverse and dynamic regulatory layer affecting all aspects of a protein from protein folding, localization, interaction and bioactivity to its stability and ultimately Stem Cell Compound Library clinical trial degradation. Therefore, each distinctly modified version of a protein, also called a protein species, and not just the initial translated version, needs to be considered this website as the functional units comprising the proteome [3]. The diversity of reversible and irreversible modifications as well as the extensive modification machinery [4] and the possibility of combinatorial effects dramatically increase proteome complexity by several orders. Organisms as different as worm, fly and man have comparable sized genomes yet show a great discrepancy in phenotypic

complexity. While splicing introduces bulk complexity it might well be that the diversity created by pinpoint posttranslational modifications accounts for the observed phenotypic differences. Hence, advanced proteomics has potential to explain phenotypes where conventional genomics fall short — but it is not easy. Every modification adds to the functional diversity of the proteome by reversibly or irreversibly converting one protein species into another that potentially is a functionally distinct species. In this regard, limited proteolysis is special as it has the unique ability to irreversibly convert one into two distinct protein species while at the same time generating new protein termini serving as attachment sites for even further PTM. Second only to ubiquitin ligases in number, proteases and their

inhibitors constitute a large enzyme family with 567 members in humans. In what has been termed the degradome, the assembly of all elements click here involved in proteolysis — proteases, inhibitors and the processed substrates — can now be specifically studied in high throughput investigations termed degradomics [5••]. Proteases modify their substrates by hydrolysis of scissile bonds releasing two peptide chains with the two amino acids adjacent to the cleaved bond now becoming carboxy-terminal or amino-terminal residues. Unlike most PTM attachment sites, the hydrolyzed peptide bond is not amenable for direct assessment. For limited proteolysis, termed processing, the site of modification is therefore determined by identification of the ‘neo’ termini of the products.