Proteomics Posttranslational modification

Meri, S. andBaumann, M., Proteomics posttranslational modifications, immune responses and current analytical tools, Biomol. Eng., 18, 213, 2001. 

The results for bacterial whole-cell analysis described here establish the utility of MALDI-FTMS for mass spectral analysis of whole-cell bacteria and (potentially) more complex single-celled organisms. The use of MALDI-measured accurate mass values combined with mass defect plots is rapid, accurate, and simpler in sample preparation then conventional liquid chromatographic methods for bacterial lipid analysis. Intact cell MALDI-FTMS bacterial lipid characterization complements the use of proteomics profiling by mass spectrometry because it relies on accurate mass measurements of chemical species that are not subject to posttranslational modification or proteolytic degradation. 

The combination of this top-down proteomics approach, which generates information on the structure of the intact protein, with a bottom-up approach for protein identification (using MS/MS data of tryptic peptides from the collected fractions) has been particularly useful for identifying posttranslational modifications, cotransla-tional processing, and proteolytic modifications in a number of proteins. Examples from our work will be shown to illustrate this hybrid methodology for proteomics analysis. 

There is now a growing interest in proteomic studies of brain synapses. Recent studies have revealed a high molecular complexity in the pre- and postsynaptic areas, with thousands of proteins [6]. An important investigation for the future is to identify posttranslational modifications, miscoded as well as misfolded proteins, likely to have an impact on different aspects of synaptic function as a response to the environment as well as to the lifestyle. The first challenge is to identify and quantify the presence and variation of different proteins in key structures of the pre- and postsynaptic areas in order to relate protein structures to synaptic function. Recently, a new model has been presented describing the molecular complexity of the synapse with important aspects in emotions, thinking, memory, and consciousness [7] (Fig. 17.2). 

ExPASy Proteomics tools (http //expasy.org/tools/), tools and online programs for protein identification and characterization, similarity searches, pattern and profile searches, posttranslational modification prediction, topology prediction, primary structure analysis, or secondary and tertiary structure prediction. 

Pathological conditions are also linked to posttranslational modifications such as oxidized histidine residues found in P-amyloid protein of Alzheimer s patients, or conformational variants in the case of prion-induced encephalopathies. The development of sensitive MS tools and proteomics techniques is playing an active role in the precise description of these mechanisms.97,98... 

How do we then envision the protein microarray as a proteomics tool We now estimate the human genome to comprise around 30,000 genes. For gene expression analysis using DNA microarrays, 1000 to 10,000 gene elements are often used. Since proteins undergo posttranslational modification (>200 different types see McDonald and Yates, 2000, Reference 40) and can occur as isoforms and multiprotein complexes, the number of protein expression elements needs to be much larger. 

Walsh CT, Garneau-Tsodikova S, Gatto GJJ (2001) Protein posttranslational modifications the chemistry of proteome diversifications. Angew Chem Int Ed 44 7342-7372... 

Proteomics is the assessment protein expression levels and can be used to monitor mRNA processing and posttranslational modifications [146, 147]. Metabonomics is... 

Proteomics Proteins Yes Measures abundance, distribution, posttranslational modifications, functions, and interactions of cellular proteins... 

The protein posttranslational modifications (PTMs) play a crucial role in modifying the end product of expression and contribute towards biological processes and diseased conditions. Important posttranslational modifications include phosphorylation, acetylation, glycosylation, ubiquitination, and nitration [Mann and Jensen, 2003], The analysis of posttranslational modifications on a proteome scale is still considered an analytical challenge [Zhou et al., 2001] because of the extremely low abundance of modified proteins among very complex proteome samples. 

One of the most useful techniques for visualization of the proteome is two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (2-D SDS-PAGE). This technique possesses unmatched resolving power for separation of proteins [2-4] and has been used extensively to analyze proteins [5-8], their regulation [9-18], and posttranslational modifications [19-22], Several tech-... 

Knowledge of protein primary sequence, quantities, posttranslational modifications (PTMs), structures, protein-protein (P-P) interactions, cellular spatial relationships, and functions are seven important attributes (see Table 4.2) needed for comprehensive protein expression analysis. It is this multifold and complex nature of protein attributes that has spawned the development of so different many proteomic technologies. Some of these challenges in proteomic analysis include defining the identities and quantities of an entire proteome in a particular spatial location (i.e., serum, liver mitochondria, brain), the existence of multiple protein forms and complexes, the evolving structural and functional annotations of the human and rodent... 

Figure 4.3. Fields of proteomic research. Proteomic research can be classified into six general research fields. Proteomic mapping and proteomic profiling constitute the first tier of proteomic analysis based upon identification and quantitation of proteins within a defined space of interest that can range from the entire organism to the protein level. The second tier of proteomic analyses is shown below involving global characterization of structure, function, posttranslational modifications, and association with other proteins (or other biochemical components).

Figure 4.13. Summary of advantages and limitations of representative proteomic platforms for protein expression analysis. The capabilities and advantages (solid line) are compared to the drawbacks (dotted lines) for each proteomic platform. Explanation of advantages and limitations are briefly highlighted here and more thoroughly discussed in the text. Abbreviations for each platform are provided in the Figure 4.1 legend and in the text. Other abbreviations used are PTMs, posttranslational modifications ID, identification.

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