Protein glycosylation is an important posttranslational modification that has profound effects on the structure and function of proteins. More than 90% human proteins have carbohydrates attached to, called glycoproteins. Because of the complex and non-templated nature of carbohydrates, it is challenging to deciphering their structures and effects on the activities of glycoproteins. The major challenges include identification of glycoproteins, sites of glycosylation, and sequencing of the saccharide moiety. Development of new tools to identify glycoproteins associated with cancer and other diseases is of current interest.
By employing a powerful glycan probing system, researchers can now selectively label glycoproteins via cellular biosynthetic pathways to insert sugar (fucose or sialic acid) analogs onto glycans followed by chemical reaction with a biotin probe for glycoprotein isolation. Using this method, a tailored glycoproteomic strategy for identifying saccharide-specific proteins is established. Following the enrichment of biotin-tagged glycoproteins by streptavidin, liquid chromatography-tandem mass spectrometry is used for glycoprotein identification and glycan site mapping (GIDmap). The power of GIDmap is demonstrated by mapping over 200 N-linked glycosylation sites from isolated sialoglycoproteins in prostate cancer cells, and 68% of these hits are previously uncharacterized glycosylation sites. Notably, over 25% of the identified proteins have known associations with tumor progression and/or metastasis, indicating the potential of GIDmap in discovering new biomarkers and therapeutic targets in cancers. This method provides a new approach that allows for comparative analysis of healthy versus disease samples.
This work was reported by Dr. Chi-Huey Wong, the President of Academia Sinica, Dr. Tsui-Ling Hsu, postdoctoral research fellow at the Genomics Research Center in Academia Sinica, and the collaborators at The Scripps Research Institute. The study will be officially published in J. Am. Chem. Soc. 129 (23), 7266-7267 on June 13, 2007. This report was also highlighted in the 11 June issue of Chemical & Engineering News of the American Chemical Society.