Glycoproteins generally exist as populations of glycosylated variants (glycoforms) of a single polypeptide. Although the same glycosylation machinery is available to all proteins that enter the secretory pathway in a given cell, most glycoproteins emerge with characteristic glycosylation patterns and heterogeneous populations of glycans at each glycosylation site. The factors that control the composition of the glycoform populations and the role that heterogeneity plays in the function of glycoproteins are important questions for glycobiology. A full understanding of the implications of glycosylation for the structure and function of a protein can only be reached when a glycoprotein is viewed as a single entity. Individual glycoproteins, by virtue of their unique structures, can selectively control their own glycosylation by modulating interactions with the glycosylating enzymes in the cell. Examples include protein-specific glycosylation within the immunoglobulins and immunoglobulin superfamily and site-specific processing in ribonuclease, Thy-1, IgG, tissue plasminogen activator, and influenza A hemagglutinin. General roles for the range of sugars on glycoproteins such as the leukocyte antigens include orientating the molecules on the cell surface. A major role for specific sugars is in recognition by lectins, including chaperones involved in protein folding. In addition, the recognition of identical motifs in different glycans allows a heterogeneous population of glycoforms to participate in specific biological interactions.

Glycosylation: heterogeneity and the 3D structure of proteins.

Publisher Summary This chapter provides a critical evaluation of the various procedures employed to extract antigens and to characterize them chemically and physically The various biological activities of the histocompatibility antigens and their use in assay systems for antigen and antibody detection and quantitation are also described in the chapter One of the most active areas of immunologic research involves the participation and interactions of various cell types in the immune response The recognition of the requirement for cell interaction in the antibody response can make the problem complicated related to the interpretation of much experimental data Excellent yields of purified rat γM macroglobulin are reported by Fisher and Canning using sucrose density gradients in the BIV zonal centrifuge This method allows for large batch processing and may be particularly useful for the isolation of γM from small animal sources A very wide range of sedimentation constants for each of the components is reported in studies of large numbers of macroglobulinemic sera (as opposed to isolated macroglobulins)

Structure and function of gamma M macroglobulins.

Solution structure of human and mouse immunoglobulin M by synchrotron X-ray scattering and molecular graphics modelling. A possible mechanism for complement activation.

Binding of Human Plasma Sialoglycoproteins by the B Cell-specific Lectin CD22 SELECTIVE RECOGNITION OF IMMUNOGLOBULIN M AND HAPTOGLOBIN

Catabolism of Asn-linked glycoproteins to monosaccharides and amino acids occurs in lysosomes. Break-down must be complete to avoid lysosomal storage diseases that occur when fragments as small as dimers are left undigested. Recent results have clarified several aspects of Asn-linked glycoprotein catabolism in mammals. First, degradation of the oligosaccharide portion is accomplished by exo-glycosidases, which act only from the nonreducing end of chains to release sugar monomers as products. In contrast, proteolysis can proceed from both end and internal points along the polypeptide to eventually yield free amino acids. A second important feature of the glycoprotein disassembly pathway is that the hydrolytic steps can be grouped into two sets of ordered reactions: I) stepwise hydrolysis of the major portion of the oligosaccharide chains by a set of exoglycosidases, and II) ordered disassembly of the protein and the oligosaccharide-to-protein linkage region. Process II can vary at a single reaction step de...

https://faseb.onlinelibrary.wiley.com/doi/pdf/10.1096/fasebj.3.14.2531691

Lysosomal degradation of Asn-linked glycoproteins.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/0014-5793%2884%2981341-1

Primary structure of the major glycans of the N-acetyllactosamine type derived from the human immunoglobulins M from two patients with Waldenström's macroglobulinemia

The well-known heterogeneity of normal and pathological immunoglobulins M was investigated in a study involving the characterization of their carbohydrate moieties. Oligosaccharide units were released from the native molecule by hydrazinolysis, and they were fractionated by affinity chromatography on a concanavalin A-Sepharose column to yield separate N-acetyl-lactosaminic-type and oligomannosidic-type structures. Further identification of these oligosaccharides was attempted by t.l.c. on silica gel and by determination of their monosaccharide compositions. A comparative study of the oligosaccharide units belonging to each population of immunoglobulin M was possible. Similarities were found in the occurrence of both types of oligosaccharide structures, and, in addition, a common double heterogeneity could be demonstrated for N-acetyl-lactosaminic-type structures: they could be resolved by affinity chromatography into bi-, tri- and tetra-antennary structures, and they also showed differences in N-acetylneuraminic acid content. Though some variations were observed in the exact composition of the oligosaccharide units within each population, it was possible to consider a representative oligosaccharide-unit composition of normal immunoglobulin M as a standard for comparison. On this basis a predominance of multi-antennary structures was observed in the more glycosylated pathological immunoglobulins M (10% carbohydrate content), whereas oligomannosidic structures were increased in pathological immunoglobulins M with a lower content of carbohydrates (7%). These variations are thought to reflect differences in the biosynthetic processing pathway of the carbohydrate units of the pathological immunoglobulins M or the enhanced expression of a molecular clone.

Comparative study of the carbohydrate moieties of normal and pathological human immunoglobulins M.

Structural basis of the heterogeneity of asparagine-linked oligosaccharides of a Waldenstrom's macroglobulinemia immunoglobulin M.

Association de I'lgM avec l'albumine dans certains cas de maladie de Waldenström

Structure primaire des chaînes glycanniques de l'inhibiteur de C1 estérase normal (C1-INH) après l'analyse en RMN à 400 MHz

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