Metabolic Labeling of Glycans with Azido Sugars for Visualization and Glycoproteomics
ABSTRACT The staggering complexity of glycans renders their analysis extraordinarily difficult, particularly in living systems. A recently developed technology, termed metabolic oligosaccharide engineering, enables glycan labeling with probes for visualization in cells and living animals, and enrichment of specific glycoconjugate types for proteomic analysis. This technology involves metabolic labeling of glycans with a specifically reactive, abiotic functional group, the azide. Azido sugars are fed to cells and integrated by the glycan biosynthetic machinery into various glycoconjugates. The azido sugars are then covalently tagged, either ex vivo or in vivo, using one of two azide-specific chemistries: the Staudinger ligation, or the strain-promoted [3+2] cycloaddition. These reactions can be used to tag glycans with imaging probes or epitope tags, thus enabling the visualization or enrichment of glycoconjugates. Applications to noninvasive imaging and glycoproteomic analyses are discussed.
- SourceAvailable from: ctgu.edu.cn[Show abstract] [Hide abstract]
ABSTRACT: Metabolic labeling of glycans with a bioorthogonal chemical reporter such as the azide enables their visualization in cells and organisms as well as the enrichment of specific glycoprotein types for proteomic analysis. This process involves two steps. Azido sugars are fed to cells or organisms and integrated by the glycan biosynthetic machinery into various glycoconjugates. The azido sugars are then covalently tagged with imaging probes or epitope tags, either ex vivo or in vivo, using an azide-specific reaction. This protocol details the syntheses of the azido sugars N-azidoacetylmannosamine (ManNAz), N-azidoacetylgalactosamine (GalNAz), N-azidoacetylglucosamine (GlcNAz) and 6-azidofucose (6AzFuc), and the detection reagents phosphine-FLAG and phosphine-FLAG-His6. Applications to the visualization of cellular glycans and enrichment of glycoproteins for proteomic analysis are described. The synthesis of the azido sugars (ManNAz, GalNAz, GlcNAz or 6AzFuc) or detection reagents (phosphine-FLAG or phosphine-FLAG-His6) can be completed in approximately 1 week. A cell metabolic labeling experiment can be completed in approximately 4 d.Nature Protocol 02/2007; 2(11):2930-44. DOI:10.1038/nprot.2007.422 · 8.36 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: An important frontier in glycoproteomics is the discovery of proteins with post-translational glycan modifications. The first step in glycoprotein identification is the isolation of glycosylated proteins from the remainder of the proteome. New enzymatic and metabolic methods are being used to chemically tag proteins to enable their isolation. Once isolated, glycoproteins can be identified by mass spectrometry. Additional information can be obtained by using either enzymatic or chemoselective reactions to incorporate isotope labels at specific sites of glycosylation. Isotopic labeling facilitates mass spectrometry-based confirmation of glycoprotein identity, identification of glycosylation sites, and quantification of the extent of modification. By combining chemical tagging for isolation and isotope labeling for mass spectrometry analysis, researchers are developing highly effective strategies for glycoproteomics. These techniques are enabling cancer biologists to identify biomarkers whose glycosylation state correlates with disease states, and developmental biologists to characterize stage-specific changes in glycoprotein expression. Next-generation methods will make functional analyses of the glycoproteome possible, including the discovery of glycoprotein interaction partners and the identification of enzymes responsible for synthesis of particular glycan structures.Current Opinion in Chemical Biology 03/2007; 11(1):52-8. DOI:10.1016/j.cbpa.2006.11.032 · 7.65 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Carbohydrate modification is a common phenomenon in nature. Many carbohydrate modifications such as some epimerization, O-acetylation, O-sulfation, O-methylation, N-deacetylation, and N-sulfation, take place after the formation of oligosaccharide or polysaccharide backbones. These modifications can be categorized as carbohydrate post-glycosylational modifications (PGMs). Carbohydrate PGMs further extend the complexity of the structures and the synthesis of carbohydrates and glycoconjugates. They also increase the capacity of the biological regulation that is achieved by finely tuning the structures of carbohydrates. Developing efficient methods to obtain structurally defined naturally occurring oligosaccharides, polysaccharides, and glycoconjugates with carbohydrate PGMs is essential for understanding the biological significance of carbohydrate PGMs. Combined with high-throughput screening methods, synthetic carbohydrates with PGMs are invaluable probes in structure-activity relationship studies. We illustrate here several classes of carbohydrates with PGMs and their applications. Recent progress in chemical, enzymatic, and chemoenzymatic syntheses of these carbohydrates and their derivatives are also presented.Organic & Biomolecular Chemistry 04/2007; 5(6):865-72. DOI:10.1039/b700034k · 3.49 Impact Factor