Scientists Dissect Cells' Sugar Coatings

Researchers at Emory University School of Medicine have adapted gene chip microarray technology to the study of glycans, with an approach they call "shotgun glycomics." The team has developed a new chemical method for attaching a fluorescent dye to glycans purified from cells. The individual glycans are separated into tiny spots fixed to glass slides.

"These slides separate and display all the glycans in the cell, so that we can test what sticks to them," says senior author David Smith, PhD, professor of biochemistry. "However, the structures of the glycans are unknown. This is why we use the word 'shotgun' to describe our quasi-random approach of studying them."

As a demonstration of the technique's utility, the team used it to identify a molecule recognized by self-reactive antibodies present in the blood of most patients with Lyme disease. Lyme disease is caused by infection with Borrelia bacteria after a tick bite, but severe cases have features of an autoimmune response, triggered by the immune system's reaction to the bacteria.

"Being able to analyze glycans in this way may lead to new diagnostics for human autoimmune disorders, and perhaps, therapies to cleanse the body of self-reactive antibodies or inhibit their pathological attack on cells," Cummings, PhD, chair of the Department of Biochemistry and co-director of the Glycomics Center, says.

Completely dissecting glycans' structures is more difficult, compared with proteins or DNA, because glycans form branched structures in which not every link is chemically the same. Scientists have estimated that cells contain hundreds or thousands of different glycans, which can be attached to proteins or lipids. When using the shotgun approach, if scientists find that proteins from the body bind to one particular glycan spot, they can then go back to that spot and determine its entire sequence, sifting out important glycans from the thousands on the slide.

The Emory team applied shotgun glycomics to red blood cells, tumour cells and brain-derived lipids. Cummings says the technique could be used to look for distinct sugar molecules displayed by cancer cells, for example. Identifying cancer-specific glycans could similarly lead to diagnostic tools or therapies, he says.; Source: Emory University