ANRV413-BI79-22 ARI 27 April 2010 21:25 Chemical Approaches to Glycobiology Laura L. Kiessling1,2 and Rebecca A. Splain1 1Department of Chemistry, 2Department of Biochemistry, University of Wisconsin–Madison, Wisconsin 53706; email: [email protected] Annu. Rev. Biochem. 2010. 79:619–53 Key Words First published online as a Review in Advance on array, glycan, glycomimetic, glycosylation, lectin, multivalency April 8, 2010 The Annual Review of Biochemistry is online at Abstract biochem.annualreviews.org Glycans are ubiquitous components of all organisms. Efforts to This article’s doi: elucidate glycan function and to understand how they are assembled 10.1146/annurev.biochem.77.070606.100917 and disassembled can reap benefits in fields ranging from bioenergy by University of Wisconsin - Madison on 07/29/10. For personal use only. Copyright c 2010 by Annual Reviews. to human medicine. Significant advances in our knowledge of glycan All rights reserved biosynthesis and function are emerging, and chemical biology ap- Annu. Rev. Biochem. 2010.79:619-653. Downloaded from arjournals.annualreviews.org 0066-4154/10/0707-0619$20.00 proaches are accelerating the pace of discovery. Novel strategies for assembling oligosaccharides, glycoproteins, and other glycoconjugates are providing access to critical materials for interrogating glycan function. Chemoselective reactions that facilitate the synthesis of glycan-substituted imaging agents, arrays, and materials are yielding compounds to interrogate and perturb glycan function and dysfunction. To complement these advances, small molecules are being generated that inhibit key glycan-binding proteins or biosynthetic enzymes. These examples illustrate how chemical glycobiology is providing new insight into the functional roles of glycans and new opportunities to interfere with or exploit these roles. 619 ANRV413-BI79-22 ARI 27 April 2010 21:25 that approximately 1% of each genome, Contents from eubacteria to archea and eukaryotes, is dedicated to sugar-processing enzymes (2). INTRODUCTION .................. 620 Moreover, these genes can be highly conserved, GLYCAN SYNTHESIS .............. 622 as the components of few other biochemical Chemical Synthesis pathways are so invariant as those responsible of Oligosaccharides ............. 623 for glycan biosynthesis (3). The importance of Engineering Enzymes this conservation is underscored by data indi- for Glycan Synthesis ............ 626 cating that defects in the glycan biosynthetic Glycoprotein and machinery in humans, known as congenital dis- Glycopeptide Synthesis ......... 628 orders of glycosylation, are rare and generally Chemical Glycobiology of have severe deleterious consequences (4). Glycolipids ..................... 629 Genomic analysis is a powerful means to Chemoselective Reactions identify enzymes that generate or degrade gly- to Modify Glycans .............. 629 cans and the proteins that recognize the gly- INTERROGATION OF can products. Still, it does not reveal what GLYCAN RECOGNITION....... 632 glycans are present in a cell or organism be- Glycan Arrays ..................... 632 cause the synthesis of glycans is not template Lectin Arrays ...................... 634 directed. As a result, elucidating the molecu- PERTURBATION OF lar mechanisms that underlie glycan function GLYCAN FUNCTION ........... 634 has been a challenge. Nevertheless, researchers Perturbation of Protein-Glycan have uncovered numerous roles for glycans, Recognition with Monovalent including those in fertilization and develop- Ligands ........................ 635 ment, hormone function, cell proliferation and Perturbation of Protein-Glycan organization, host-pathogen interactions, and Recognition with Multivalent the inflammatory and immune responses (3). Ligands ........................ 637 These findings are providing additional impe- Perturbation of Glycan Assembly . 640 tus to devise new approaches that meet the chal- Exploiting Alternative Substrates lenges of elucidating and manipulating glycan in Glycan Biosynthesis .......... 643 function. Illuminating Glycan Biosynthesis . 644 The increased appreciation for the ubiquity CONCLUSION ..................... 646 of glycans and their importance to human health has spawned the field of chemical glycobiology. Because of the complexities of by University of Wisconsin - Madison on 07/29/10. For personal use only. Glycan: a generic glycans, their study has compelled researchers term referring to a INTRODUCTION to pursue interdisciplinary approaches. Since Annu. Rev. Biochem. 2010.79:619-653. Downloaded from arjournals.annualreviews.org monosaccharide, oligosaccharide, Glycans, which are compounds that include the pioneering contributions of 1902 Nobel polysaccharide, or its monosaccharides, oligosaccharides, polysac- Laureate Emil Fischer, it has been apparent conjugate (e.g., charides, and their conjugates, are critical that our understanding of glycan function glycolipid, constituents of all organisms. Members of a can be advanced using approaches that span glycoprotein, or other glycan subset, the polysaccharides, are the most biology and chemistry. The nucleation of the glycoconjugate) abundant organic compounds on Earth. Gly- discipline of chemical biology is yielding new Glycoconjugate: one coconjugates (e.g., peptidoglycan, glycolipids, and innovative strategies to probe glycan func- or more saccharide units (glycone) glycoproteins) also are prevalent. In humans, tion (5). Indeed, there has been an explosion covalently linked to a for example, half of all proteins are glycosy- of research in this area. As a result, this review noncarbohydrate lated (1). Consistent with glycan abundance in cannot provide comprehensive coverage of the moiety (aglycone) nature, data from genomic sequencing indicate field but rather offers an overview of select 620 Kiessling · Splain ANRV413-BI79-22 ARI 27 April 2010 21:25 advances that illustrate the unique contribu- agents can be used for purposes ranging from Glycobiology: the tions and exciting opportunities within the imaging glycans to cross-linking them to their study of sugars in field of chemical glycobiology. binding partners. Together, these chemical biological systems, The state of the art of chemical glycobiology strategies are illuminating the molecular including their is focused on key questions: How are glycans mechanisms that underlie glycan function. structures, made and degraded, what are their biological biosynthesis, and physiological roles roles once in place, and how can these roles be exploited? To address these questions, Interrogation researchers have employed the complementary a Glycan- b Cell strategies of interrogation and perturbation binding protein Lectin (Figure 1). The interrogation strategy strives to understand endogenous interactions between Antibody natural glycans and their cognate enzymes or Glycan binding partners. Access to naturally occurring array and novel glycans provides the means to examine protein-glycan or enzyme-glycan in- teractions. Arrays composed of glycoconjugates Surface (Figure 1a) or lectins (Figure 1b) are valuable tools for interrogating protein-binding speci- ficity or cellular glycosylation patterns. With Perturbation the complementary perturbation approach, in- c e hibitors, analogs, or other nonnatural substrates Lectin can serve as probes of both the biosynthesis and Inhibitor the biological roles of glycans. Indeed, novel nonnatural oligosaccharide mimics or syn- thetic glycoconjugates can inhibit or encourage specific biomolecular interactions within cells Glycosyl- transferase and organisms (Figure 1c,d ). Moreover, compounds have been identified that can block key steps within glycan biosynthetic pathways d Cell (Figure 1e). Finally, carbohydrate analogs can Normal Inhibitor sugar be incorporated into glycans using the cellular Lectin biosynthetic machinery (Figure 1f ). Such by University of Wisconsin - Madison on 07/29/10. For personal use only. −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−→ f Nonnatural sugar Figure 1 Annu. Rev. Biochem. 2010.79:619-653. Downloaded from arjournals.annualreviews.org Interrogation and perturbation in chemical glycobiology. (a) Glycan arrays have been developed to interrogate the binding specificities of lectins (blue), antibodies (green), and other glycan-binding proteins (orange). (b) Lectin arrays can be used to fingerprint cell-surface or pathogen glycosylation Multivalent ligand patterns. Monovalent (c) and multivalent (d ) ligands for glycan-binding proteins can perturb protein- glycan interactions. (e) Inhibitors can prevent key steps in glycan biosynthesis, thereby reducing the production of specific glycan structures. ( f ) Nonnatural monosaccharides can serve as substrates for biosynthetic enzymes and thereby be incorporated into glycans. www.annualreviews.org • Chemical Approaches to Glycobiology 621 ANRV413-BI79-22 ARI 27 April 2010 21:25 GLYCAN SYNTHESIS glycolipids, glycosylphosphatidylinositol an- Defined oligosaccharides and glycoconjugates chors, proteoglycans, and polysaccharides are are critical for unraveling the function of gly- influenced by accessibility of the nucleotide Lectin: a glycan- binding protein of cans. Obtaining these entities from natural donors, but the mechanisms governing the reg- nonimmune origin sources is difficult because their production ulation of these pathways are still being eluci- generally involves the participation of multiple dated. Thus, it is difficult to obtain sufficient transporters and enzymes (6). This complex- quantities of glycans