Asparagine-linked glycoproteins

Swainsonine (1) is of great biochemical interest since it is a potent and specific inhibitor of both lysosomal a-mannosidase and mannosidase II, which are involved in the cellular degradation of polysaccharides and in the processing of asparagine-linked glycoproteins, respectively [1]. 

Dan, A. Ito, Y. Ogawa, T., A Convergent and Stereocontrolled Synthetic Route to the Core Pentasaccharide Structure of Asparagine-Linked Glycoproteins. J. Org. 

The discovery that dolichol phosphates and pyrophosphates (diphosphates) are carriers for oligosaccharides in eukaryotic cells initiated the modem era of glycoprotein biochemistry. These lipid-linked oligosaccharides are precursors for the carbohydrate side chains of the asparagine-linked glycoproteins. Because of this common precursor, all of the side chains of these glycoproteins share the same carbohydrate core, shown within the dashed box in Figure 16-la. 

Additional evidence for a glucagon-stimulated plasma membrane component of System A comes from the results of Barber et al. (65) who showed that the asparagine-linked, glycoprotein biosynthesis inhibitor tunicamycin blocked the hormone induction of System A. As shown previously for cycloheximide or puromycin (59, 61) if tunicamycin was added to hepatocytes after the hormone-mediated induction of transport activity had begun, inhibition of further stimulation occurred within 1 hour (65). These results demonstrate that the System A-associated glycoprotein responsible for the increased uptake activity must be continuously synthesized if the stimulation of transport is to be maintained. 

FIGURE 9.26 The carbohydrate tnoiedes of glycoproteins may be linked to the protein via (a) serine or threonine residues (in the O-linked saccharides) or (b) asparagine residues (in the N-linked saccharides), (c) N-Linked glycoproteins are of three types high mannose, complex, and hybrid, the latter of which combines structures found in the high mannose and complex saccharides. 

Figure 47-4. Structures of the major types of asparagine-linked oligosaccharides. The boxed area encloses the pentasaccharide core common to all N-linked glycoproteins. (Reproduced, with permission, from Kornfeld R, Kornfeld S Assembly of asparagine-linked oligosaccharides. Annu Rev Biochem 1985 54 631.)...

Fibrinogen (factor I, 340 kDa see Figures 51-1 and 51-4 and Tables 51-1 and 51-2) is a soluble plasma glycoprotein that consists of three nonidentical pairs of polypeptide chains (Aa,Bpy)2 covalently linked by disulfide bonds. The B(3 and y chains contain asparagine-linked complex oligosaccharides. All three... 

The complex oligosaccharides comprising the Y and T antennae of three glycoproteins have been studied by c.d. spectroscopy. Five antennae were studied in all, because two of the proteins have two closely related forms. The c.d. for the three fundamental oligosaccharides are given in Fig. 36. These are asparagine-linked glycopeptides, and the intense, conservative c.d. band that results from the interaction between the two amides has already been discussed in Section III,2. Fig. 36 shows that the c.d. spectra... 

Endo-2-acetamido-2-deoxy-)3-D-glucosidase has been used in structural studies of glycopeptides.30 The enzyme cleaves the linkage between the two 2-amino-2-deoxyglucose residues that constitute the chitobiose residue linked to L-asparagine in glycoproteins containing... 

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