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  • Biosynthesis of Glycans in Eukaryotes

    Eukaryotic cells synthesize many different kinds of glycoconjugates including glycoproteins, glycolipids and proteoglycans. Different cell compartments are equipped with specific synthetic enzymes that are used to build and modify the glycans. Once synthesized, the glycoconjugates reside in different cell locations or are secreted out of the cell.

    In the lumen of the endoplasmic reticulum (ER) N-Glycans are transferred to specific asparagine residues of the nascent polypeptide, a process intimately associated with protein folding (1). As the protein migrates through the ER and Golgi apparatus, specific enzymes trim back the glycan chain, while other enzymes add new monosaccharides to the glycan structure (2). Once in the Golgi the glycoproteins are sorted for distribution to their final destination: to specific cell compartments (such as the vacuole), to the cell surface, or to the extracellular space for secretion (3), as seen in the figure below.

    A schematic diagram representing the synthesis of N-glycans in a eukaryotic cell. A pre-assembled glycan is transferred from a lipid carrier (Dol-p-p) to a nascent protein. The glycan is trimmed and then extended in the Golgi. Glycosyltransferases use activated sugars (nucleotide-sugars) as donors for the extension reactions.

    References

    1. Caramelo JJ, et al. (2007) Semin. Cell. Dev. Biol. 18(6):732-42. PMID: 17997334
    2. Roth J. (2002) Chem Rev. 102(2):285-303. PMID: 11841244
    3. Yamashita K, et al. (1999) Biochim Biophys Acta. 1473(1):147-60. PMID: 10580135
    • Overview of Glycobiology

      Learn about the core sequences and common modifications of N-linked and O-linked glycans in this video. Analysis of these glycans and/or peptide portions of the glycoprotein can be accomplished with the use of deglycosylation enzymes, which are explained in detail. Unlike other chemical deglycosylation methods, enzymatic treatment is much gentler and can provide complete sugar removal with no protein degradation.

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    • Identification and Characterization of Protein Glycosylation

      Here we illustrate the use of glycosidases for the analysis of a model glycoprotein: recombinant human chorionic gonadotropin beta (hCGβ), which carries both N-glycans and O-glycans in this video. The technique requires only simple instrumentation and typical consumables, and it can be readily adapted to the analysis of multiple glycoprotein samples.

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    • Elucidating the Complexity of Heparin Oligosaccharide Analysis

      Learn more about the structural elucidation of complex and diverse heparin oligosaccharides using Bacteroides Heparinase I, II and III in combination with downstream mass spec analysis.

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