RICHARD CUMMINGSGlycans are part of an elaborate communication system vital for cellular recognition, cell-cell interactions, protein transport, immune defense, and more. These three-dimensional sugar structures attached to most proteins encode a vast amount of information that researchers are just beginning to tap (See “Getting Your Sugar Fix,” The Scientist, April 2015). “With glycans, there are several levels of information,” says Carlito Lebrilla, a chemist at the University of California, Davis: the number of positions carrying a glycan, the location of each of those glycosites, and the chemical composition and branching structure of each glycan. Despite being the most common posttranslational modification, the complexity of glycosylation has left glycobiology lagging behind other fields, such as protein sequence analysis and genomics. But that’s changing, as researchers identify glycosylation as an important player in many diseases, including cancer. A handful of aberrant glycoproteins are already used as biomarkers to track responses to cancer treatment, but most techniques to identify these biomarkers are not sensitive enough to be useful early in disease.
Mass spectrometry, which can identify the chemical composition of glycans in a sample, also precisely measures relative abundances of certain glycans and intact glycopeptides. Researchers are now tailoring their sample preparation methods and mass spectrometry–based techniques to maximize the amount of information collected in each experiment, while keeping the variability low and the throughput high enough for clinical use. The Scientist spoke with some of these researchers about how they use mass spectrometry to take the measure of glycans.
Investigator: David Muddiman, Professor, Department of Chemistry, North Carolina State University
Project: To investigate changes in serum glycan signatures over different stages of ovarian cancer.
Problem: One easy and widely used way to compare glycan regulation in healthy and diseased states is to enzymatically release all the glycans in a given sample from their proteins and analyze them in bulk. Researchers use stable-isotope labeling mass spectrometry to identify up- or downregulation of certain glycans between samples. Glycans from one sample receive a light isotope label, such as C12, while a heavier carbon isotope such as C13 is attached in the other sample, and the relative abundance of each ion reveals the relative abundances of the labelled glycans. One common way to attach these isotopes to ...
