Positional proteomics in the era of the human proteome project on the doorstep of precision medicine.

Proteolytic processing is a pervasive and irreversible post-translational modification that expands the protein universe by generating new proteoforms (protein isoforms). Unlike signal peptide or prodomain removal, protease-generated proteoforms can rarely be predicted from gene sequences. Positional proteomic techniques that enrich for N- or C-terminal peptides from proteomes are indispensable for a comprehensive understanding of a protein's function in biological environments since protease cleavage frequently results in altered protein activity and localization. Proteases often process other proteases and protease inhibitors which perturbs proteolytic networks and potentiates the initial cleavage event to affect other molecular networks and cellular processes in physiological and pathological conditions. This review is aimed at researchers with a keen interest in state of the art systems level positional proteomic approaches that: (i) enable the study of complex protease-protease, protease-inhibitor and protease-substrate crosstalk and networks; (ii) allow the identification of proteolytic signatures as candidate disease biomarkers; and (iii) are expected to fill the Human Proteome Project missing proteins gap. We predict that these methodologies will be an integral part of emerging precision medicine initiatives that aim to customize healthcare, converting reactive medicine into a personalized and proactive approach, improving clinical care and maximizing patient health and wellbeing, while decreasing health costs by eliminating ineffective therapies, trial-and-error prescribing, and adverse drug effects. Such initiatives require quantitative and functional proteome profiling and dynamic disease biomarkers in addition to current pharmacogenomics approaches. With proteases at the pathogenic center of many diseases, high-throughput protein termini identification techniques such as TAILS (Terminal Amine Isotopic Labeling of Substrates) and COFRADIC (COmbined FRActional DIagonal Chromatography) will be fundamental for individual and comprehensive assessment of health and disease.

Eckhard U ，Marino G ，Butler GS ，Overall CM ... -  《-》

Current trends and challenges in proteomic identification of protease substrates.

Proteolytic cleavage is a ubiquitous, irreversible, posttranslational modification that changes protein structure and function and plays an important role in numerous physiological and pathological processes. Over the last decade, proteases have become increasingly important clinical targets because many of their inhibitors are already used in the clinic or in various stages of clinical testing. Therefore, a better understanding of protease action and their repertoires of physiological substrates can not only provide an important insight into their mechanisms of action but also open a path toward novel drug design. Historically, proteases and their substrates were mainly studied on a case-by-case basis, but recent advancements in mass spectrometry-based proteomics have enabled proteolysis studies on a global scale. Because there are many different types of proteases that can operate in various cellular contexts, multiple experimental approaches for their degradomic characterization had to be developed. The present paper reviews the mass spectrometry-based approaches for determining the proteolytic events in complex biological samples. The methodologies for substrate identification and the determination of protease specificity are discussed, with a special focus on terminomic strategies, which combine peptide labeling and enrichment.

Vizovišek M ，Vidmar R ，Fonović M ，Turk B ... -  《-》

N- and C-terminal degradomics: new approaches to reveal biological roles for plant proteases from substrate identification.

Proteolysis is an irreversible post-translational modification that regulates many intra- and intercellular processes, including essential go/no-go decisions during cell proliferation, development and cell death. Hundreds of protease-coding genes have been identified in plants, but few have been linked to specific substrates. Conversely, proteolytic processes are frequently observed in plant biology but rarely have they been ascribed to specific proteases. In mammalian systems, unbiased system-wide proteomics analyses of protease activities have recently been tremendously successful in the identification of protease substrate repertoires, also known as substrate degradomes. Knowledge of the substrate degradome is key to understand the role of proteases in vivo. Quantitative shotgun proteomic studies have been successful in identifying protease substrates, but while simple to perform they are biased toward abundant proteins and do not reveal precise cleavage sites. Current degradomics techniques overcome these limitations by focusing on the information-rich amino- and carboxy-terminal peptides of the original mature proteins and the protease-generated neo-termini. Targeted quantitative analysis of protein termini identifies precise cleavage sites in protease substrates with exquisite sensitivity and dynamic range in in vitro and in vivo systems. This review provides an overview of state-of-the-art methods for enrichment of protein terminal peptides, and their application to protease research. These emerging degradomics techniques promise to clarify the elusive biological roles of proteases and proteolysis in plants.

Huesgen PF ，Overall CM 《-》

Identification of proteolytic products and natural protein N-termini by Terminal Amine Isotopic Labeling of Substrates (TAILS).

Doucet A ，Kleifeld O ，Kizhakkedathu JN ，Overall CM ... -  《-》

Positional proteomics: is the technology ready to study clinical cohorts?

Lange PF ，Schilling O ，Huesgen PF 《-》