les_8 - CHAPTER VII. POSTTRANSLATIONAL MODIFICATIONS VII.1....

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121 CHAPTER VII. POSTTRANSLATIONAL MODIFICATIONS VII.1. INTRODUCTION Upon translation, a eukaryotic protein is often destined for further processing and modification. The former includes proteolytic cleavage and peptide splicing (e.g. cut-off of signal peptides, maturation of insulin,…). As for post-translational modifications (PTM), over 300 forms have been reported. Stable modifications (such as lipidation, glycosylation,…) are essential for maturation of newly synthesized proteins into proper structural and functional states (e.g. recruitment to the plasma membrane, formation of disulfide bridges,…). Many other covalent modifications are inducible, reversible and can be recognized by motifs. These PTMs such as phosphorylation, ubiquitination, sumoylation, acetylation,… play important roles in regulating protein function. PTM of a protein can be very complex. Indeed, a single protein can undergo Single- or multi-site modification : modification at several AA positions 1 type of modification (e.g. phosphorylation and acetylation on 1 protein) competitive same-site modifications (e.g. Histone 3 can be methylated or acetylated at the same site) 1 of the same modifications on 1 AA e.g. mono- and poly-ubiquitination, mono-, di-, tri-Methylation. Figure 1. Examples of proteins that can undergo multi- site and different PTM. A= acetylation , M= methylation , P= phosphorylation, S= sumoylation, U= ubiquittination
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122 As a result, PTMs can alter the function of the modified protein. A PTM can induce a new conformational state (=allosteric regulation), regulate the activity or change the subcellular localization of the protein. However, it has become more and more evident that many of the PTMs create inducible binding sites for specific PPI domains. These domains can then ‘decode’ the state of the protein and help the cell to respond accurately to changes in the external and internal environments that led to these PTMs (Table 1). Table 1. Modification-specific recognition by protein domains. Figure 2. Examples of different modifications on the same AA residu.
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123 PTMs can be classified in 4 groups: 1. addition of functional groups: phosphorylation, acetylation, glycosylation, methylation, lipoylation, ADP-ribosylation,… 2. addition of other proteins or peptides: ubiquitination/ubiquitinylation, sumoylation, neddylation, ISGylation,… 3. changes of chemical nature of AA: deimination, deamidation 4. structural changes: disulfide bridges, proteolytical cleavages In this chapter, only a selected number of PTMs within the first two classes will be discussed. Besides their characteristics and functions, also some methods to detect PTMs will be introduced. Amongst these detection methods is mass spectrometry (MS). Indeed, in the last decade, PTMs are more and more examined by MS, as a PTM results
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This note was uploaded on 05/28/2010 for the course WE BIBI000000 taught by Professor Johangrooten during the Spring '10 term at Ghent University.

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les_8 - CHAPTER VII. POSTTRANSLATIONAL MODIFICATIONS VII.1....

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