Glycoscience assists in the development of new drugs and biofuels, but for greater benefits, advances in the field must occur, according to Transforming Glycoscience: A Roadmap for the Future, a report released earlier this month by the National Academy of Sciences. The report evaluates the current state of glycoscience research, notes its contributions and limitations, and describes the improvements needed to better understand glycans and take advantage of the field. A variety of analytical techniques are currently used in studying glycans, which are macromolecules comprised of linked sugars. Improving the use of these techniques will be crucial to glycoscience’s role in such areas as medicine, energy and materials science.

Glycoscience examines the structures and functions of sugars. Glycans are created by enzymatic reactions that do not originate from a particular template, which complicates their study and manipulation. Despite the difficulties, the report cites potential benefits of glycoscience, which include providing a more comprehensive view of information provided by genomics and proteomics, according to David Walt, chair of the committee that published the report, Robinson Professor of Chemistry and Howard Hughes Medical Institute Professor at Tufts University. “For example, many cellular proteins have glycans attached to them, and these glycans can affect protein functions,” he said. “Glycans cover cells, and they are also integral components of cell walls.”

The report states that in order to maximize the potential of glycoscience, a toolbox of techniques to provide different information about glycans must be adopted. “Researchers need to have a range of techniques to synthesize glycans, to identify and characterize glycan structures, and to study and understand glycan functions,” explained Dr. Walt. “For example, some tools and techniques can provide information on the sequence of saccharide units that form a glycan or on a glycan’s three-dimensional structure. Other techniques can be used to study the interactions of glycans with proteins or other molecules. In other cases, imaging techniques (for example, attaching fluorescent labels to glycans) are used to show glycan locations or trafficking.”

Glycans can assist with early disease detection and drug development in that they are part of many biological interactions, including those of a virus or bacteria in human cells, and with generating an immune response. The report also indicates that glycoscience could lead to more efficient biofuels production, which is hindered by plant cell walls’ resistance to degradation. The report also notes that because glycan-based polymers are continuously produced in plants, they could address issues of cost and supply with petroleum-based polymers.

Glycan synthesis is a major issue for advancing glycoscience. Glycan synthesis is performed chemically, enzymatically and chemoenzymatically, but there is currently no routine process for glycan synthesis, which prohibits the production of large quantities. Another limitation is that there are no general methods for complex carbohydrate preparation, so synthesis is time consuming. Collections of glycoconjugates are often difficult to prepare because they generally exist in low concentrations. Synthesis is further complicated by the fact that it is hard to control glycoform formation in cell culture. The report calls for progress on advancing glycan synthesis, including researching the genes involved in glycan synthesis, improving methods for selective glycosylation and minimizing purification steps. Current experimental techniques include one-pot multistep solution-phase glycan synthesis, solid-phase glycan synthesis and fluorous tagging. “We need better synthetic technologies in the long run,” said Geert-Jan Boons, another committee member and the Franklin Professor of Chemistry at the Complex Carbohydrate Research Center at the University of Georgia. “We need automated synthesis to create the diversity that is found in nature.”

Tools to analyze glycan structure also have limitations. NMR, MS and crystallography are three techniques currently used for analysis of glycan structure that are discussed in the report. Improvements in these areas are also needed for glycoscience to progress. NMR is particularly useful in providing general information about anomeric configuration, although the technique lacks the sensitivity to provide more specific information. NMR can, however, accurately characterize large quantities of one glycan. “If you have one glycan in sufficient quantities, NMR can exactly determine its structure,” explained Dr. Boons. “But if you have a cell, and you strip off all the glycans, you have an enormous amount of glycans, and it’s virtually impossible to separate all these glycans into individual components and have sufficient quantities for NMR.”

MS is another technique used to analyze primary glycan structures. MS is less capable of defining exact structures than NMR but can analyze complex molecules. Its main disadvantage is that it quantifies components with each other instead of absolutely, which would allow independent assessment of glycans. To achieve this, the report recommends that a set of well-defined oligosaccharide standards be created. MS has been used to determine anomeric configurations of medium-size oligosaccharides, but advances in its sensitivity are needed to analyze anomeric configurations of small fragments.

NMR and crystallography are two techniques used for analysis of glycans’ three-dimensional structure. Isotopic enrichment would improve atomic-level characterization of oligosaccharides and polysaccharides by NMR, as NMR cannot analyze larger glycan molecules. Among crystallography’s capabilities are the detection of water molecules in hydrogen bonds that NMR cannot detect and the analysis of intermolecular interactions. The report cites the need for the development of crystallographic techniques specifically designed to analyze complex glycans. The report suggests further development of methods for total disassembly of large glycans, determining five- or six-membered ring forms, analyzing anomeric configuration and providing linkage information.

Analytical techniques have been useful in advancing glycoscience, but no technique alone can help the field progress. The report outlines the need for a faster, more streamlined process for synthesis specifically designed for glycans, as well as improved structural techniques to understand how glycans interact with proteins, how enzymes synthesize and degrade glycans, and where specific glycan structures in cells or tissues are located. In addition, the report urges the broader scientific community to work together to achieve such progress and includes a list of research goals for five-, 10- and 15-year periods. Goals include the establishment of routine procedures for synthesis of all types of glycans, the implementation of a toolbox for determining the structures of carbohydrates and complex molecules, and the development of imaging methods to study the structure, localization and metabolism of glycans. “To advance glycoscience and achieve the report’s recommendations will require contributions from scientists in multiple areas and across the mandates of multiple government agencies,” said Dr. Walt.