Glycoproteins cell-walls

FIGURE 8.18 Dolichol phosphate is an initiation point for the synthesis of carbohydrate polymers in animals. The analogous alcohol in bacterial systems, undecaprenol, also known as bactoprenol, consists of 11 isoprene units. Undecaprenyl phosphate delivers sugars from the cytoplasm for the synthesis of cell wall components such as peptidoglycans, lipopolysaccharides, and glycoproteins. Polyprenyl compounds also serve as the side chains of vitamin K, the ubiquinones, plastoquinones, and tocopherols (such as vitamin E). 

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. 

The presence and biological importance of oligosaccharide structures, usually as components of glycolipids and glycoproteins, in bacterial capsular and cell-wall polysaccharides, in mammalian cell membranes, in cytoplasm, and in extracellular fluids, are now well documented. They are important constituents in... 

Cassab, G.I., Nieto-Sotelo, J., Cooper, J.B., Van Holst, G.-J. Varner, J.E. (1985). A developmentally regulated hydroxyproline-rich glycoprotein from the cell walls of soybean coats. Plant Physiology, 77, 532-5. 

We propose that the tomato fruit B subunit is the archetypal member of a new class of plant cell wall proteins, which we have named AroGPs, for Aromatic Amino Acid Rich GlycoProteins. AroGPs have the following characteristics ... 

The plant cell wall contains different types of polysaccharides, proteins (structural glycoproteins and enzymes), lignin and water, as well as some inorganic components (1, 14-16). The plant cell suspensions, however, grow as a population of cells with a primary cell wall(17). The main components of these walls are cellulose-free polysaccharides and pectic polysaccharides in particular, which constitute 1/3 of their dry weight. (18). Some fragments, e g. methanol, acetic, ferulic and p-cumaric acids, are connected with the pectic polysaccharides by ester bonds with the carboxylic and hydroxylic groups. 

The components of the plant cell wall (8-21) are the middle lamella (intercellular substance), the primary wall, and the secondary wall. The middle lamella is the pectic layer between cells and holds adjoining cells together as do membrane carbohydrates. The primary wall is thin (1-3 pm) and flexible containing cellulose, hemicelluloses, pectins, and glycoproteins. This wall provides mechanical strength, maintains cell shape,... 

HoodKR, BaasiriRA, Fritz SE, Hood EE. Biochemical and tissue print analyses of hydroxyprohne-rich glycoproteins in cell walls of sporophytic maize tissues. Plant Physiol 1991 96 1214-1219. 

Figure 9.12 Deoxy derivatives. These contain one less oxygen atom than the monosaccharide from which they are derived. 2-Deoxyribose is a most important deoxy pentose and is a major constituent of deoxyribonucleic acid (DNA). Deoxy hexoses are widely distributed among plants, animals and microorganisms especially as components of complex polysaccharides. Examples are rhamnose (6-deoxymannose), a component of bacterial cell walls, and fucose (6-deoxygalactose), which is often found in glycoproteins and is an important constituent of human blood group substances.

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