Sweet Attachments

Isolating and detecting glycosylated proteins

May 1, 2008
Jeffrey M. Perkel
<figcaption> Credit: © Hybrid Medical Animation / Photo Researchers, Inc.</figcaption>
Credit: © Hybrid Medical Animation / Photo Researchers, Inc.

When it comes to posttranslational modifications, phosphorylation gets most of the attention, but glycosylation is more widespread. Nearly all cell-surface and secreted proteins are adorned with oligosaccharides, which affect cell-cell interactions, immune cell function, and antigenicity. Changes in glycosylation patterns have been linked to cancer, making glycoproteins ripe for biomarker discovery.

Yet studying sugar modifications is a difficult proposition. "If the glycoprotein has 10 or 12 glycans and each is different, that's a heck of a lot of work," says Ajit Varki, codirector of the Glycobiology Research and Training Center at the University of California, San Diego, and executive editor of Essentials of Glycobiology. "It could take a postdoc a year. So you don't want to get into that unless you have some evidence that the glycan is important."

Protein-linked glycosylation events come in two primary flavors: N-linked glycans attach via asparagine residues, whereas O-linked glycans attach through serine or threonine. Unlike proteins and nucleic acids, there is no template to determine the order, composition, linkages, and branching arrangement of glycan chains. And you'll need to find and isolate the glycoproteins in the first place - a problem that often requires a tailored approach. The Scientist asked five glycobiologists how they do that in their own research.

Read about their work by clicking on the glycosylation user profiles in the related articles box located to the right.