An overview of the background for proteomics and a description of the present state of art are given with a description of the main strategies in proteomics. The advantages and limitations of the two major strategies, 2D-gel based and LC-MS based, are discussed and a combination for the two, CeLC-MS is described. A number of challenging problems which have been solved using different proteomics strategies including the advantage of organell enrichment or modifications specific peptide isolation to get deeper into the proteome are described. Finally the present status and future needs discussed.
Diabetes mellitus is a complex metabolic disorder characterized by chronic hyperglycemia due to absolute or relative lack of insulin. Though great efforts have been made to investigate the pathogenesis of diabetes, the underlying mechanism behind the development of diabetes and its complications remains unexplored. Cumulative evidence has linked mitochondrial modification to the pathogenesis of diabetes and its complications and they are also observed in various tissues affected by diabetes. Proteomics is an attractive tool for the study of diabetes since it allows researchers to compare normal and diabetic samples by identifying and quantifying the differentially expressed proteins in tissues, cells or organelles. Great progress has already been made in mitochondrial proteomics to elucidate the role of mitochondria in the pathogenesis of diabetes and its complications. Further studies on the changes of mitochondrial protein specifically post-translational modifications during the diabetic state using proteomic tools, would provide more information to better understand diabetes.
The low abundance and highly hydrophobic nature of most membrane proteins make their analysis more difficult than that for common soluble proteins. Successful membrane protein identification is largely dependent on the sample preparation including the enrichment and dissolution of the membrane proteins. A series of conventional and newly developed methods has been applied to the enrichment of low-abundance membrane proteins at membrane and/or protein levels and to the dissolution of hydrophobic membrane proteins. However, all the existing methods have inherent advantages and limitations. Up to now, there has been no unique method that can universally be employed to solve all the problems and more efforts are needed in improving sample preparation for the analysis of membrane proteomes.
The human serum proteome is closely associated with the state of the body. Endogenous peptides derived from proteolytic enzymes cleaving on serum proteins are widely studied due to their potential application in disease-specific marker discovery. However, the reproducibility of peptidome analysis of endogenous peptides is significantly influenced by the proteolytic enzymes within body fluids, thereby limiting the clinical use of the endogenous peptides. We comprehensively investigated the N and C terminus of endogenous peptides using peptidomics. The cleavage site patterns of the N and C terminus and adjacent sites from all the identified endogenous peptides were highly conserved under different sample preparation conditions, including long-term incubation at 37°C and pretreatment with repeated freeze-thaw cycles. Furthermore, a distinguishable cleavage site pattern was obtained when a different disease serum was analyzed. The conserved cleavage site pattern derived from proteolytic enzymes holds potential in highly specific disease diagnosis.
Protein phosphorylation is a ubiquitous protein post-translational modification, which plays an important role in cellular signaling systems underlying various physiological and pathological processes. Current in silico methods mainly focused on the prediction of phosphorylation sites, but rare methods considered whether a phosphorylation site is functional or not. Since functional phosphorylation sites are more valuable for further experimental research and a proportion of phosphorylation sites have no direct functional effects, the prediction of functional phosphorylation sites is quite necessary for this research area. Previous studies have shown that functional phosphorylation sites are more conserved than non-functional phosphorylation sites in evolution. Thus, in our method, we developed a web server by integrating existing phosphorylation site prediction methods, as well as both absolute and relative evolutionary conservation scores to predict the most likely functional phosphorylation sites. Using our method, we predicted the most likely functional sites of the human, rat and mouse proteomes and built a database for the predicted sites. By the analysis of overall prediction results, we demonstrated that protein phosphorylation plays an important role in all the enriched KEGG pathways. By the analysis of protein-specific prediction results, we demonstrated the usefulness of our method for individual protein studies. Our method would help to characterize the most likely functional phosphorylation sites for further studies in this research area.
Valid animal models are useful for studying the pathophysiology of specific disorders, such as neural disease, diabetes and cancer. Previous molecular phylogeny studies indicate that the tree shrew is in the same order as (or a close sister to) primates, and thus may be an ideal model in which to study human disease. In this study, the proteome of liver and muscle tissue in tree the shrew was identified by combining peptide fractionation and LC-MS/MS identification. In total, 2146 proteins were detected, including 1759 proteins in liver samples and 885 proteins in skeletal muscle samples from the tree shrew. Further sub-source analysis revealed that nearly half of the identified proteins (846 proteins and 418 proteins) were derived from human database. In this study, we are the first to describe the characteristics of the proteome from the liver and skeletal muscle of the tree shrew. Phylogenetic tree analysis based on these proteomic data showed that the tree shrew is closer to primates (human) than to glires (the mouse and rat).
Studies on cell signaling pay more attention to spatial dynamics and how such diverse organization can relate to high order of cellular capabilities. To overview the specificity of cell signaling, we integrated human receptome data with proteome spatial expression profiles to systematically investigate the specificity of receptors and receptor-triggered transduction networks across 62 normal cell types and 14 cancer types. Six percent receptors showed cell-type-specific expression, and 4% signaling networks presented enriched cell-specific proteins induced by the receptors. We introduced a concept of "response context" to annotate the cell-type dependent signaling networks. We found that most cells respond similarly to the same stimulus, as the "response contexts" presented high functional similarity. Despite this, the subtle spatial diversity can be observed from the difference in network architectures. The architecture of the signaling networks in nerve cells displayed less completeness than that in glandular cells, which indicated cellular-context dependent signaling patterns are elaborately spatially organized. Likewise, in cancer cells most signaling networks were generally dysfunctional and less complete than that in normal cells. However, glioma emerged hyper-activated transduction mechanism in malignant state. Receptor ATP6AP2 and TNFRSF21 induced rennin-angiotensin and apoptosis signaling were found likely to explain the glioma-specific mechanism. This work represents an effort to decipher context-specific signaling network from spatial dimension. Our results indicated that although a majority of cells engage general signaling response with subtle differences, the spatial dynamics of cell signaling can not only deepen our insights into different signaling mechanisms, but also help understand cell signaling in disease.
Holo glutaredoxin (Grx) is a homo-dimer that bridges a [2Fe-2S] cluster with two glutathione (GSH) ligands. In this study, both monothiol and dithiol holo Grxs are found capable of transferring their iron-sulfur (FeS) cluster to an apo ferredoxin (Fdx) through direct interaction, regardless of FeS cluster stability in holo Grxs. The ligand GSH molecules in holo Grxs are unstable and can be exchanged with free GSH, which inhibits the FeS cluster transfer from holo Grxs to apo Fdx. This phenomenon suggests a novel role of GSH in FeS cluster trafficking.