Proteomics studies

The second step in 2D electrophoresis is to separate proteins based on molecular weight using SDS-PAGE. Individual proteins are then visualized by Coomassie or silver staining techniques or by autoradiography. Because 2D gel electrophoresis separate proteins based on independent physical characteristics, it is a powerful means to resolve complex mixtures proteins (Fig. 2.1). Modem large-gel formats are reproducible and are the most common method for protein separation in proteomic studies. 

Current proteomics studies rely almost exclusively on 2D gel electrophoresis to resolve proteins before MALDI-TOF or ESI-MS/MS approaches. A drawback of the 2D gel approach is that it is relatively slow and work intensive. In addition, the in-gel proteolytic digestion of spots followed by mass spectrometry is a one-at-a-time method that is not well suited for high throughput studies. Therefore, considerable effort is being directed towards alternate methods for higher throughput protein characterization. 

Proteomics is an interdisciplinary science that includes biology, bioinformatics, and protein chemistry. The purpose of this book is to provide the reader with an overview of the types of questions being addressed in proteomics studies and the technologies used to address those questions. The first chapter is a concise outline of the field as it presently stands. The second chapter provides an overview of the use of 2D-gel electrophoresis and mass spectrometry to identify proteins, as well as post-translational... 

Hamler, R. L. Zhu, K. Buchanan, N. S. Kreunin, P. Kachman, M. T. Miller, F. R. Lubman, D. M. A two-dimensional liquid-phase separation method coupled with mass spectrometry for proteomic studies of breast cancer and biomarker identification. Proteomics 2004,4, 562-577. 

Premstaller, A., Oberacher, H., Walcher, W., Timperio, A.M., Zolla, L., Chervet, J.P., Cavusoglu, N., van Dorsselaer, A., Huber, C.G. (2001). High-performance liquid chromatography-electrospray ionization mass spectrometry using monolithic capillary columns for proteomic studies. Anal. Chem. 73, 2390-2396. 

Chen, J., Gao, J., Lee, C.S. (2003b). Dynamic enhancements of sample loading and analyte concentration in capillary isoelectric focusing for proteome studies. J. Proteome Res. 2, 249-254. 

Gu, S Du, Y Chen, J., Liu, Z Bradbury, E.M., Hu, C.A., Chen, X. (2004). Large-scale quantitative proteomic study of PUMA-induced apoptosis using two-dimensional liquid chromatography—mass spectrometry coupled with amino acid-coded mass tagging. J. Proteome Res. 3, 1191 1200. 

Wehr, T. (2002). Multidimensional Liquid Chromatography in Proteomic Studies. LCGCNorth America 20, 954-962. 

This chapter has presented several comprehensive 2DLC approaches combining a first-dimension IEX separation and a second-dimension RP separation for the analysis of complex protein mixtures typical in proteomics studies. Online ESI-TOF/MS detection provided sensitive detection and valuable qualitative information (MW) for proteins eluting from the MDLC system. Coordinated fraction collection and subsequent MS analysis of peptides produced by proteolysis of the fractions provided in-depth information on protein identification and a mechanism... 

At least two driving forces have contributed to the recent increased use and development of multidimensional liquid chromatography (MDLC). These include the high resolution and peak capacity needed for proteomics studies and the independent size and chemical structure selectivity for resolving industrial polymers. In this regard, separation science focuses on a system approach to separation as individual columns can contribute only part of the separation task and must be incorporated into a larger separation system for a more in-depth analytical scheme. 

Many diseases are characterized by the expression of specific proteins1 in some cases, malignant cells yield unique protein profiles when total cellular protein extracts are analyzed by proteomic methods such as two-dimensional gel electrophoresis or matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS).2 High-throughput proteomic studies may be useful to differentiate normal cells from cancer cells, to identify and define the use of biomarkers for specific cancers, and to characterize the clinical course of disease. Proteomics can also be used to isolate and characterize potential drug targets and to evaluate the efficacy of treatments. 

In summary, studies carried out with tissue surrogates25 highlight some of the problems that must be overcome before proteins extracted from FFPE tissues can be used for routine proteomic studies. First, these studies demonstrate that reversal of protein-formaldehyde adducts does not assure quantitative extraction of proteins from FFPE tissues or vice-versa. It may ultimately turn out that there is no one universal method that can accomplish both tasks, but that instead, each step will need to be optimized separately. Studies with tissue surrogates also suggest that failure to quantitatively extract the entire protein component from FFPE tissues may result in sampling bias due to the preferential extraction of certain proteins. This behavior may be linked to protein physical properties, such as the isoelectric point. The results of our... 

The tissue surrogates described here clearly represent a simplification of real FFPE tissues. However, they represent a useful and efficient construct for the evaluation and optimization of tissue extraction conditions for proteomic studies. More informative studies will likely be realized by using more complex tissue surrogates, which can be created by incorporating additional proteins into lysozyme solutions. Tissue surrogates comprised of up to five proteins have been successfully analyzed by MS (Fowler, unpublished data). Additionally, RNA, DNA, lipids, or carbohydrates can be added at nanomolar to millimolar concentrations to increase the complexity of the model system to better mimic whole tissue. The use of these more complex tissue surrogates should facilitate the development of protein recovery protocols optimal for proteomic investigation. 

High-throughput proteomic methods hold great promise for the discovery of novel protein biomarkers that can be translated into practical interventions for the diagnosis, treatment, and prevention of disease. These approaches may also facilitate the development of therapeutic agents that are targeted to specific molecular alterations in diseases such as cancer. In many cases, malignant cells yield unique protein profiles when total protein extracts from such cells are analyzed by 2-D gel electrophoresis or mass spectrometry (MS) methods. Such proteomic studies have the potential to provide an important complement to the analysis of DNA and mRNA extracts from these tissues.1... 

Several proteomic studies using archival FFPE tissues have been reported in recent years. Some involve the analysis of very small tissue samples prepared... 

A number of proteomic studies on archival material have utilized Liquid Tissue (Expression Pathology, Inc., Gaithersburg, MD), a commercial protein extraction kit for FFPE tissue.4,9,25-28 This kit is also based upon HIAR techniques and shares a similar work flow to the methods already discussed. Thin, typically 5-10pM, sections are cut from paraffin tissue blocks, the paraffin is removed, and the tissue deparaffinized and rehydrated in alcohols and distilled water before microdissection. The cellular material is then suspended in Liquid Tissue buffer and heated at 95°C for 90 min. Trypsin is added, and the material is digested overnight at 37°C prior to reduction with DTT and analysis by LC-MS/MS.26... 

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