Academic literature on the topic 'Glycosidic Bond Stability'

Most eukaryotic proteins, some bacterial and many viral proteins carry structurally diverse carbohydrates that are covalently attached through N- or O-glycosidic bonds to the side chains of asparagine, serine, threonine, hydroxylysine, tyrosine, and hydroxyproline. In nature, N-linked glycoproteins are assembled by post-translational, enzymatic attachment of a common oligosaccharide having the composition Glc3Man9GlcNAc2 to the side chain of asparagine. This saccharide is then modified enzymatically, thereby giving structural variation to the part remote from the protein. However, N-linked glycoproteins have a common pentasaccharide core (Manα3(Manα6)Manβ4GlcNAcβ4GlcNAc) in which the chitobiose moiety (GlcNAcβ4GlcNAc) is bound to asparagine. By contrast, O-linked glycoproteins are built up by sequential attachment of monosaccharides by different enzymes to hydroxylated amino acids in the protein, and therefore no common core is formed. Thus, N-acetyl-α-D-galactosamine attached to serine and threonine is found in mucin secreted from epithelial cells. β-D-Xylosyl serine is found in many proteoglycans, whereas β-D-galactosyl hydroxylysine is common in collagen found in connective tissue. α-L-Fucosyl residues linked to serine and threonine are found in fibrinolytic and coagulation proteins. N-Acetyl-β-D-glucosamine attached to serine and threonine occurs frequently in glycoproteins located in the nucleus and cytoplasm, whereas glycoproteins produced by yeast have α-D-mannosyl residues linked to serine and threonine. Larger structures are usually formed by attachment of additional saccharides to the O-linked 2-4 when found in glycoproteins. Structures 5,10, and 11 can also carry additional monosaccharides. In recent years numerous glycoproteins have been isolated and characterized, but the roles for the protein-bound carbohydrates have only just begun to be unravelled. It is now well established that glycosylation affects both the physiochemical properties and the biological functions of a glycoprotein. For instance, glycosylation has been found to influence uptake, distribution, excretion, and proteolytic stability. It is also known to have important roles in communication between cells and in attachment of bacteria and viruses to the host. Efforts to understand the role of glycosylation of proteins, or to develop glycopeptides as tools in drug discovery and drug design, have led to substantial progress in development of methodology for the synthesis of glycopeptides during the last decades.