Mammalian glycoproteins carry thousands of different glycan strucures which comprise mainly the N-linked (β-N-acetyl-D-glucosamine-Asn) and O-linked (α-N-acetyl-D-galactosamine-Ser or -Thr) types of sugar chains (N-glycans and O-glycans, respectively). Minor structures are also found as a single O-G1cNAc (β-N-acetyl-D-glucosamineSer/Thr-linked) or as O-Fuc-linked (α-L-fucose-Thr/Ser), O-Glc-linked (β-D-glucose-Thr/Ser) and O-Man-linked (α-D-mannose-Ser) glycan chains. Other major classes of glycosylated mammalian proteins include the collagens and proteoglycans; the latter may also carry N- and O-glycans typically found on glycoproteins. O- or N-glycans are known to change during growth, development, oncogenic transformation and differentiation of cells. The different sizes, chemical, physical and antigenic properties of glycans determine the variety of biological functions which are now slowly being unraveled. Since glycoproteins are involved in many aspects of the immune system, in fertilization, cell adhesion, hormone action and receptor functions as well as in bacterial and viral binding and infectivity and other functions (see chapter 9), it is not surprising that altered carbohydrate structures lead to abnormal functions and altered behavior of diseased cells.
KeywordsSialic Acid Diseased Cell Sugar Chain Glycan Structure Oncogenic Transformation
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