Glycobiology: Toward Understanding the Function of Sugars Raymond A. Dwek The Glycobiology Institute, Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK Received July 20, 1995 (Revised Manuscript Received October 28, 1995) Contents 1. Introduction and Background 683 1.1. Biological Macromolecules 683 1.2. Glycoproteins 684 1.3. Glycobiology 684 1.4. Technology Developments 684 1.5. There Is No Single Unifying Function for Oligosaccharides 684 2. What Does a Typical Glycoprotein Look like? 685 2.1. Implication of the Conformations and Dynamics of Protein Surface Oligosaccharides in Protein Function 685 2.2. Molecular Dynamics (MD) Simulation of Man 9 GlcNAc 2 OH 686 2.3. The Core Conformation of the Oligosaccharide in N-Linked Glycoproteins Is Independent of the Protein 686 2.4. Outer Arm Conformation of the Oligosaccharide 687 2.5. Dynamic Sugar Model of RNase B 687 2.6. Consequences of Protein Side-Chain Flexibility on the Presentation of the Oligosaccharide 687 2.7. Biological Implications 688 3. Some Factors Which Control Protein Glycosylation 688 3.1. The Primary Peptide Structure Determines the Number and Location of Potential Glycosylation Sites 688 3.2. Structure and Diversity of N-Linked Glycans 689 3.3. Structure of O-Linked Glycans 689 3.4. Cell Type Influences Glycosylation 689 3.5. The 3D Structure of the Protein Influences the Extent and Type of Glycosylation 690 3.6. Generation of Glycoforms 691 4. Oligosaccharide Technology 692 4.1. Release of Glycans from Glycoprotein 692 4.2. Labeling of the Released Glycans To Enable Their Detection in Subsequent Procedures 693 4.3. Profiling the Pool Glycans To Determine the Types of Glycans Present and Their Relative Molar Properties 693 4.4. Structural Analysis 694 5. Characteristics of Protein Glycosylation 695 5.1. Importance of the Overall Protein Conformation in Determining Glycosylation 695 5.2. Effect of Local Protein ConformationsGlycosylation Shows Site Specificity 695 5.3. Glycosylation Is Protein-Specific, Site-Specific, and Tissue/Cell-Specific 697 6. Glycosylation Site Occupancy Can Modulate Enzyme Activities 698 6.1. The Multimolecular Interaction of tPA with Plasminogen and Fibrin Is Modulated by Glycosylation 699 6.2. Variable Glycosylation Site Occupancy on Carbohydrate-Deficient Glycoprotein Syndrome (CDGS) 700 7. Some Structural Roles for Oligosaccharides 701 7.1. Glycosyl-Phosphatidylinositol (GPI) Anchors 701 7.2. Structure/Function Relationships in IgG 702 8. Oligosaccharide Recognition 703 8.1. Specific Interactions with Animal Lectins 703 8.2. Neural Glycosylation and Recognition 705 8.3. Major Histocompatibility Complex (MHC) Restricted Recognition of Glycopeptides by T-Cells 706 8.4. Recognition of Oligosaccharides by Stimulated T-Cells 707 9. Glycosylation in Disease 707 9.1. The IgG Molecule 707 9.1.1. Site-Specific Glycosylation of IgG 707 9.1.2. IgG Glycoforms Associated with Rheumatoid Arthritis 708 9.1.3. Glycosylation Changes on the IgG Molecule Are “Disease Restricted” and Are an Important Factor in Rheumatoid Arthritis 708 9.1.4. Structural Changes in IgG Fc on Loss of Galactose 709 9.1.5. Functional Implications of IgG Glycoforms 710 9.1.6. Modeling of the Possible Interaction between Agalactosyl IgG Fc and MBP 711 9.1.7. Ca 2+ -Dependent Binding of MBP to IgG Is Mediated by the Agalactosyl Fc Glycoforms 712 9.1.8. MBP Activation of Complement by Agalactosyl IgG Glycoforms 712 9.1.9. MBP and Agalactosyl IgG Are Present in Synovial Fluid 713 10. Glycosylation Inhibitors as Antiviral Agents 713 10.1. Glycosphingolipids 715 10.2. Glycosphingolipid Storage Disorders 717 11. Concluding Remarks 717 12. Acknowledgments 718 13. References 718 1. Introduction and Background 1.1. Biological Macromolecules Four major classes of macromolecules in biology are DNA, proteins, carbohydrates, and lipids. Carbohy- drates differ from the other two classes of biological polymers in two important characteristics: they can be highly branched molecules, and their monomeric 683 Chem. Rev. 1996, 96, 683-720 0009-2665/96/0796-0683$25.00/0 © 1996 American Chemical Society