Of glycoprotein

Glycoproteins or mucoproieins. Compounds of proteins with carbohydrates. All glycoproteins contain a hexosamine and usually sulphate, ethanoate and glucuronic acid. The carbohydrate-protein linkages are, in some cases covalent and in others of the salt type. Aqueous solutions of glycoproteins are extremely viscous. 

Puromycin. Puromycin (19), elaborated by S. alboniger (1—4), inhibits protein synthesis by replacing aminoacyl-tRNA at the A-site of peptidyltransferase (48,49). Photosensitive analogues of (19) have been used to label the A-site proteins of peptidyltransferase and tRNA (30). Compound (19), and its carbocycHc analogue have been used to study the accumulation of glycoprotein-derived free sialooligosaccharides, accumulation of mRNA, methylase activity, enzyme transport, rat embryo development, the acceptor site of human placental 80S ribosomes, and gene expression in mammalian cells (51—60). 

Glycoconjugates. Another class of carbohydrates are the glycoconjugates (14), composed of glycoproteins, proteoglycans, peptidoglycans, and glycohpids. 

W. J. Leimar2, Biochemistry of Glycoproteins andProteogJycans, Plenum Press, New York, 1980. 

Lennarz, W. J., 1980. The Biochemistry of Glycoproteins and Proteoglycans. New York Plenum Press. 

Long-chain polyisoprenoid. molecules with a terminal alcohol moiety are called, polyprenols. The dolichols, one class of polyprenols (Figure 8.18), consist of 16 to 22 isoprene units and, in the form of dolichyl phosphates, function to carry carbohydrate units in the biosynthesis of glycoproteins in animals. Polyprenyl groups serve to anchor certain proteins to biological membranes (discussed in Chapter 9). 

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 9.27 The O-Unked saccharides of glycoproteins appear in many cases to adopt extended conformations that serve to extend the functional domains of these proteins above the membrane surface. (Adaptedfrom Jentofi, N., 1990, Trends in Biochemical Sciences 15 291-294.)... 

Several drugs in current medical use are mechanism-based enzyme inactivators. Eor example, the antibiotic penicillin exerts its effects by covalently reacting with an essential serine residue in the active site of glycoprotein peptidase, an enzyme that acts to cross-link the peptidoglycan chains during synthesis of bacterial cell walls (Eigure 14.17). Once cell wall synthesis is blocked, the bacterial cells are very susceptible to rupture by osmotic lysis, and bacterial growth is halted. 

Concanavalin A is a plant lectin from the jack bean (Canavalia ensiformis) which binds with high affinity to mannose residues of glycoproteins. Concanavalin A is known to stimulate the tyrosine kinase activity of the INSR (3-subunit with consecutive activation of kinases downstream the insulin receptor (IRS, PI 3-kinase). It is believed that Concanavalin A stimulates the activation and autophosphorylation of the INSR kinase through aggregation of the receptor, although the precise mechanism of action is unclear. 

The methodology employed for the study of glycoproteins is somewhat different in that it is not just the saccharide sequence that is required but the position at which it is joined to the peptide backbone. 

Figure 5.31 LC-electrospray-MS-MS spectrum of the column eluate at around 22 min in the analysis of the peptide mixture from the tryptic digest of glycoprotein TIME-EA4 from silkworm diapause eggs. Reprinted from Bioorg. Med. Chem., 10, Kurahashi, T., Miyazaki, A., Murakami, Y., Suwan, S., Franz, T., Isobe, M., Tani, M. and Kai, H., Determination of a sugar chain and its linkage site on a glycoprotein TIME-EA4 from silkworm diapause eggs by means of LC-ESI-Q-TOF-MS and MS/MS , 1703-1710, Copyright (2002), with permission from Elsevier Science.

A biomolecular system of glycoproteins derived from bacterial cell envelopes that spontaneously aggregates to form crystalline arrays in the mesoscopic range is reviewed in Chapter 9. The structure and features of these S-layers that can be applied in biotechnology, membrane biomimetics, sensors, and vaccine development are discussed. 

D-Arabinose Gum arabic. Plum and cherry gums. Constituent of glycoproteins. ... 

Amino Sugars (Hexosamines) Are Components of Glycoproteins, Gangliosides, Glycosaminoglycans... 

The disorders listed are discussed further in other chapters. The table lists examples of mutations affecting receptors, a transporter, an ion channel, an enzyme, and a structural protein. Examples of altered or defective glycosylation of glycoproteins are also presented. Most of the conditions listed affect the plasma membrane. 

Many studies have been conducted in an attempt to define the precise roles oligosaccharide chains play in the functions of glycoproteins. Table 47-2 summarizes results from such studies. Some of the functions listed... 

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