Post -translational glycosylation

C. Most membrane proteins undergo post-translational glycosylation to improve their interactions with the aqueous environment and to protect them from degradation by proteases. 

It is, however, well established that membrane glycoproteins and secreted proteins are glycosylated during the synthesis of their peptide backbone,12,1,-221 although post-translational glycosylation has also been reported.222-2233 The question arises as to whether these proteins... 

Blom N, Sicheritz-Ponten A, Gupta, R, Gammeltoft S, Brunak S. 2004. Prediction of post-translational glycosylation and phosphorylation of proteins from the amino acid sequence. Proteomics 4 1633-1649. 

Fig. 5. Topology and common structural features of GPCRs from class A. The characteristic seven transmembrane domains, which are presumably a-helical, are shown as numbered cylinders TMI-VII. These are connected by intracellular loops ICLI-III and extracellular loops, ECLI-III. A conserved disulfide links ECLI and ECLII. The residues that define common sequence motifs, as discussed in the text, are denoted by white circles. Post-translational glycosylation and palmitoylation modifications are depicted at the N- and C-termini, respectively (see text for additional discussion and references).

Blom, N., T. Sicheritz-Ponten, R. Gupta, S. Gammeltoft and S. Brunak (2004), Prediction of Post-Translational Glycosylation and Phosphorylation of Proteins from the Amino Acid Sequence , Proteomics Vol. 4 1633-1649. 

Nieman, H., Boschek, B., Evans, D., Rosig, M., Tamura, T., and Klenk, H., 1982, Post-translational glycosylation of coronavirus glycoprotein El—Inhibition by monensin, EM BO J. 1 1499-1504. 

While electrospray is used for molecules of all molecular masses, it has had an especially marked impact on the measurement of accurate molecular mass for proteins. Traditionally, direct measurement of molecular mass on proteins has been difficult, with the obtained values accurate to only tens or even hundreds of Daltons. The advent of electrospray means that molecular masses of 20,000 Da and more can be measured with unprecedented accuracy (Figure 40.6). This level of accuracy means that it is also possible to identify post-translational modifications of proteins (e.g., glycosylation, acetylation, methylation, hydroxylation, etc.) and to detect mass changes associated with substitution or deletion of a single amino acid. 

Both ChEs undergo several post-translational modifications, including glycosylation and glycosylphosphatidy-linositolation (GPI), phosphorylation and carbamylation. 

Post-translation modification Changes that occur to proteins after peptide-bond formation has occurred, e.g. glycosylation and acylation. 

Post-translational modification of proteins plays a critical role in cellular function. For, example protein phosphorylation events control the majority of the signal transduction pathways in eukaryotic cells. Therefore, an important goal of proteomics is the identification of post-translational modifications. Proteins can undergo a wide range of post-translational modifications such as phosphorylation, glycosylation, sulphonation, palmitoylation and ADP-ribosylation. These modifications can play an essential role in the function of the protein and mass spectrometry has been used to characterize such modifications. 

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