A new technique for capturing glycosylated proteins, developed by a researcher at Simon Fraser University, has provided fresh insight into the relationship between the structure and function of these biomolecules, knowledge that could advance fields from immunology to cancer research.

From bacteria to humans, many cell surface proteins are decorated with glycans: sugar moieties whose biological function is still not completely understood. Scientists can study glycosylated proteins by breaking apart cells, then using agarose beads coated with hydrazide molecules to attract the glycans and therefore their associated proteins. But this technique has limitations. “The cell surface proteins are typically very hydrophobic and difficult to dissolve into an aqueous solution,” says Bingyun Sun, who recently moved to SFU from the Institute for Systems Biology in Seattle. She also points out that many cell surface proteins have only a few glycans on them, reducing the chance they will stick to the beads.

Five years ago, Sun and her team tried a counterintuitive approach: they used the enzyme trypsin to cut glycosylated proteins into dozens of pieces before exposing them to the collector beads. Although this technique only captures a few pieces from each protein — the ones with glycans on them — Sun found the pieces were large enough to compare with databases and determine which proteins they came from. In general, the technique was more sensitive than previous ones.

In their latest paper, published in PLoS ONE, Sun and her team used the technique on cell surface proteins from mouse embryonic stem cells. They found that transporter proteins used to bring objects into the cell had very few glycans compared to receptor proteins used for signalling. This structure/function relationship had not been previously observed, and could be of great help to glycan researchers, such as those trying to distinguish cancerous cells from healthy ones, or bacterial cells from human ones. “I think we will see some follow-up results very soon,” says Sun.