SPOT Grabs, Tags Carbohydrates

A new technique for immobilizing and tagging biological carbohydrates could lead to a much more convenient way to analyze complex sugars than is currently possible.

The method, solid-phase oligosaccharide tagging (SPOT), was developed by Ole Hindsgaul and coworkers at Carlsberg Laboratory, in Copenhagen, who demonstrated its use by analyzing commercial versions of two glycolipid-derived complex carbohydrates (Angew. Chem. Int. Ed., published online May 19, dx.doi.org/10.1002/anie.200600642).

Protein and lipid glycosylation (modification with carbohydrates) plays a key role in function and disease, and researchers would like to better understand the relationship between the structure and activity of these attached biological carbohydrates. But they are highly variable and extraordinarily complex in structure, often having multiple branches and stereocenters, and procedures for their structural analysis are difficult and specialized.

SPOT could help address this problem. It's a simple set of reactions for immobilizing carbohydrates on beads, tagging them with fluorescent and other groups, and releasing them for analysis. Immobilizing carbohydrates on solid supports is not new, but SPOT's immobilization, tagging, and release chemistry is easier to carry out than earlier approaches.

"The key feature of the method really is its simplicity: There is no requirement for experience in the handling of oligosaccharides," Hindsgaul and coworkers note. Nevertheless, "the paper is clearly only a model study, and there remains a lot of work to be done before SPOT enters the mainstream of glycomics," they add.

"With further development, SPOT has the potential to greatly facilitate the detection, quantification, and analysis of saccharides released from glycoconjugates," says professor of biological chemistry Gerald W. Hart of Johns Hopkins University School of Medicine. "The key promise of this emerging method is that it will allow biologists with little training in glycosciences to reliably analyze glycans on their favorite molecules."

James C. Paulson, director of the Consortium for Functional Glycomics at Scripps Research Institute, says SPOT's novel aspect is its use of "a reactive nitrogen to introduce tags useful for detection and purification of glycans. The chemistries are robust and efficient, features that are critical for working with small amounts of biological materials. This method will undoubtedly find important applications in glycan analysis, although it is still at an early stage."

A third researcher, who agreed to comment only without attribution, expresses more doubts about the technique's significance. SPOT's chemistry "is not really all that new," he says. "Sequencing carbohydrates is an important problem, and this may be one of the technical details that lead to an eventual solution, but is this the one breakthrough? It's a step in the right direction, but we'll see what comes afterwards."

However, professor of biochemistry and molecular biology Michael Pierce of the University of Georgia sees the work as "a promising start to making it possible for commonplace laboratories to do glycan sequencing. It's a proof of concept, and now the question is, 'Can it be applied to specific biological samples?' I think there will be quite a lot of interest in the glycobiology community to get this method to work."