Carbohydrate Chemistry: Happy Birthday To Microarrays

Carbohydrate microarrays have become essential screening tools for revealing the functions of biomolecules that interact with sugars, providing essential information on the mechanisms of diseases. The devices, which were developed a decade ago, are each made up of solid substrates displaying hundreds of different oligosaccharides (also called glycans) or carbohydrate-containing macromolecules.

In 2002, four initial types were designed and constructed: polysaccharide and glycoconjugate microarrays by Denong Wang’s group at Columbia University (Nat. Biotech., DOI: 10.1038/nbt0302-275); monosaccharide chips by Milan Mrksich and coworkers at the University of Chicago (Chem. Biol. 2002,9, 443); natural and synthetic oligosaccharide arrays by Ten Feizi’s group at Imperial College London (Nat. Biotech., DOI: 10.1038/nbt735); and synthetic oligosaccharide arrays on microtiter plates by a group from Scripps Research Institute in California led by Chi-Huey Wong, now president of Academia Sinica, in Taiwan (Chem. Biol. 2002,9, 713; J. Am. Chem. Soc., DOI: 10.1021/ja020887u).

The carbohydrate microarray field has matured since then, thanks in part to the establishment of research centers that specialize in the technology—for example, the Carbohydrate Microarray Facility at Imperial College and the Consortium for Functional Glycomics based at Scripps and at Emory University.

Carbohydrate arrays can be constructed with either underivatized or chemically modified oligosaccharides. Columbia’s Wang, for example, has specialized in making arrays by attaching underivatized saccharides covalently or noncovalently to substrates.

“The use of underivatized saccharides for microarray construction has the advantage of preserving the native structures of the carbohydrate molecules,” Wang says, “but requires a ready-to-use microarray surface with appropriate surface chemistry.”

Because desired surface chemistries for unmodified oligosaccharides are often difficult to produce, microarrays made from modified carbohydrates have become far more popular.

For instance, Feizi and her coworkers at Imperial College’s Carbohydrate Microarray Facility construct microarrays by releasing oligosaccharides from glycosylated proteins or polysaccharides and tagging them with lipids, forming “neoglycolipids.” These constructs are immobilized noncovalently on solid matrices for binding experiments. The researchers currently use arrays that display about 800 unique oligosaccharides. There’s no charge to users for screening limited numbers of samples at the facility, which is supported by the Wellcome Trust.

Researchers at the Consortium for Functional Glycomics also use derivatized oligosaccharides to construct arrays. But in their case, the oligosaccharides are attached covalently to glass slides via amine linkers. The current arrays each have 610 synthetic oligosaccharides, including oligo­saccharides with up to 37 sugar units. The arrays are available at no cost to users through the support of the National Institute of General Medical Sciences, says James C. Paulson, who led development of the arrays. The devices are produced at Scripps, and screening data are analyzed at Emory.

Carbohydrate microarrays have not been commercialized, owing in part to difficulties encountered in optimizing and standardizing the way oligosaccharides are immobilized and their density and distribution on array surfaces. Nevertheless, they are proving valuable in a range of applications.

In one such application, microarray analysis of the pandemic H1N1 flu virus uncovered a potential mechanism linking viral receptor binding to disease severity. Another oligosaccharide array study identified immunogenic carbohydrate moieties of anthrax spores. And carbohydrate array studies of neutralizing antibodies that target oligosaccharides from HIV-infected patients are aiding the design of HIV vaccines.

“Carbohydrate microarray technology has come of age as a tool in the biological sciences,” Feizi says.