Synthetic sugars enhance the functional glycomics toolkit

Abstract

Glycosaminoglycan-protein interactions are an important frontier for discovering new mechanisms of cellular regulation by complex sugars. The integration of the 'chemical glycomics' strategies of synthetic chemistry, arrays and biological assays shows that the precise pattern of sugar sulfation dictates the specificity of a sugar's function.Understanding the complex functions of the glycome-the repertoire of sugars expressed by cells, tissues and organisms-is a substantial challenge in the postgenome era. Glycosaminoglycans (GAGs) are an important class of complex sugars whose structurally diverse polysaccharide chains contain large amounts of information 1 that is linked to an extensive range of biological functions. However, an understanding of the mode of glycan specificity underlying these functions has proven elusive 1 . A paper by Gama et al. published in this issue of Nature Chemical Biology reports the synthesis of a set of chondroitin sulfate (CS) tetrasaccharides whose interactions and bioactivity provide evidence for a 'sulfation code' in which recognition of selected proteins is conferred by specific sequences 2 . The use of a unique combination of synthetic chemistry, microarray technology and biological assays indicates a way forward for future studies aimed at understanding the selectivity and functions of GAG structures.Questions concerning the specificity of GAG-protein interactions abound and can only be definitively addressed using fully characterized compounds. The difficulty of obtaining such structures from nature is a significant bottleneck, and the development of tools and technologies to evaluate these molecules lags behind that of genomics and proteomics. Fortunately, the field is rapidly changing 3 . For instance, chemical synthesis avoids many of the purification problems that plague natural-products chemistry. In addition, large-scale interrogation of glycan-proteins is now possible, allowing the discovery of new molecular liaisons. In particular, recent studies describe new approaches for obtaining arrayed displays of both natural 4 and synthetic 5 GAG structures from the heparan sulfate-heparin family.Initial efforts in glycosynthesis, such as those by Lopin et al., demonstrated that chondroitin saccharides can be effectively synthesized in a highly convergent and efficient manner 6 . Gama et al. 2 extend these concepts by emphasizing the value of integrative science in NIH Public Access

Enabling methodology for the end functionalisation of glycosaminoglycan oligosaccharides

“…As a consequence, oligosaccharides in protein-GAG complexes do not occupy hydrophobic pockets, but sit on the protein surface with only a few intermolecular contacts, 7,8 making solution-phase structure determination of these complexes very challenging. Despite a wealth of chemical and genetic evidence to suggest that control of the fine structure of GAGs including their detailed sulfation patterns is crucial for their function in vivo, [9][10][11][12] there have been comparatively few studies of these interactions at the molecular level due to a lack of enabling chemical tools, and even fewer studies where these interactions are placed in a broader context as part of the emerging field of glycomics. 13 The four basic classes of GAGs [heparin/heparan sulfate (HS), chondroitin sulfate (CS)/dermatan sulfate (DS), keratan sulfate (KS) and hyaluronan (HA)] are produced by a common biosynthetic pathway in which the linear alternating uronic acid/hexosamine polymeric chain is extended in a stepwise fashion.…”

Structural Characterization of Glycosaminoglycan Carbohydrates Using Ultraviolet Photodissociation

“…Glycosaminoglycans (GAGs), linear polysaccharides composed of repeating hexosamine and uronic acid disaccharides, are complex molecules that participate in a number of biological processes ranging from tissue development to inflammation. − GAG structural complexity arises from variations in their degree of polymerization, extent of saccharide sulfation, and uronic acid stereochemistry. Such modifications are responsible for the specific interactions GAGs have with proteins, with misregulation of modifications implicated in a number of genetic diseases, including Alzheimer’s and cancer. − Development and quality control of GAG therapeutics also relies on a detailed knowledge of GAG structures. , In 2008, heparin, an anticoagulant drug, contaminated with oversulfated chondroitin sulfate resulted in 81 deaths . Detailed structural characterization of GAGs is therefore essential yet still impeded by a number of technical challenges.…”

Harnessing glycomics technologies: Integrating structure with function for glycan characterization

“…Integration of these techniques (functional genetics, glycan synthesis, and glycan arrays) with analytical approaches is critical for a number of reasons (as summarized in recent reviews []). In general, as described above, multiple glycan sequences can bind to a given protein.…”