Eukaryotic proteins, glycosylation

Protein glycosylation occurs mainly on serine and asparagine residues,but can also occur on hydroxylysine and hydroxyproline (Scheme 15). Glycosylation is very important in the endoplasmic reticulum and Golgi apparatus and can be involved in cell signaling. Many of the membrane-bound proteins and excreted proteins are glycosylated. Protein glycosylation is important in all forms of eukaryotes. ... 

In the first Section, the dolichol pathway of protein glycosylation is introduced, and the reader is made familiar with the various reactions in the formation of the lipid and carbohydrate moieties of lipid-linked saccharides. Three different classes of compound are known so far (a) isoprenoid alcohol esters of monosaccharide monophosphates, such as D-mannosyl and D-glucosyl (dolichol phosphate), (b) such isoprenoid alcohol esters of saccharide diphosphates as dolichol diphosphate linked to 2-acetamido-2-deoxy-D-glucose and to oligosaccharides, and (c) retinol (D-mannosyl phosphate). The dolichol-linked sugars occur in all eukaryotes. 

Eukaryotic Proteins Targeted for Secretion Are Synthesized in the Endoplasmic Reticulum Proteins That Pass through the Golgi Apparatus Become Glycosylated... 

Translation in prokaryotes (H2) Protein glycosylation (H5) Translation in eukaryotes (H3)... 

The CBS prediction server also provides services for predicting O-glycosylation sites (NetGly) in mammalian proteins (http //www.cbs.dtu.dk/services/NetQGly-2.0/) and phosphorylation sites (NetPhos) in eukaryotic proteins (http //www.cbs.dtu.dk/ services/NetPhos/). Paste the query sequence and click the Submit Sequence button to receive the predicted results. NetOGly returns tables of potential versus threshold assignments for threonine and serine residues as well as a plot of O-glycosylation potential versus sequence position. NetPhos returns tables of context (nanopeptides, [S,T,Y] + 4 residues) and scores for serine/threonine/tyrosine predictions. 

Although bacterial hosts can be useful for protein production, E. coli and other prokaryotic expression systems have some limitations. For example, they are incapable of posttranslational modifications such as glycosylation and as a consequence many eukaryotic proteins produced in prokaryotic expression systems are nonfunctional (Rai and Padh, 2001). However, in the case of most peptides, including self-assembling peptides, such modifications are currently not required. Of course, this limitation may have implications for future... 

The above example also gives an indication of the relative importance of carbohydrate analysis. Without question, protein glycosylation is the most complex of all posttranslational modifications made in eukaryotic cells, the importance of which cannot be underestimated. For many compounds, glycosylation can readily affect protein solubility (as influenced by folding), protease resistance, immunogenicity, and pharmacokinetic/pharmacodynamic profiles (i.e., clearance and efficacy) [36], Typical analytical methodologies used to assess carbohydrate content are also listed in Table 2. 

Glycosylation. Carbohydrate modifications of proteins (glycosylation) are key factors in modulating protein structures and functions within cells. Glycosylation affects probably more than half of all proteins in a eukaryotic cell [40]. In the extracellular environment, the oligosaccharide moieties of... 

The major advantage of using mammalian cells to produce heterologous eukaryotic proteins are that the expressed proteins are correctly folded and glycosylated to near native structures [ 173]. Because of these unique post-trans-lational modifications, various mammalian expression systems have been reported time to time for the production of therapeutic proteins [173-176]. However, the high cost of cell culture, low productivity (5-50 pg cell 1 day-1), and difficulty in growing in large scale imposes serious restrictions on their... 

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