Glycoscience Program Highlights
Glycosylation is the chemical addition of a sugar to a protein or lipid molecule, which can modify the function of the protein or lipid and its role in a biological process. Glycosylation includes a huge number of modifications with very different structures, resulting in an enormous variety of biological consequences. Although glycosylation is critical to the development and function of multicellular organisms, it is also the least understood protein modification. This is because of the large diversity of glycan structures, which makes glycosylation modifications difficult to identify, and varying biological concentrations, which makes them difficult to detect. Current methods used to study glycosylation don’t allow for the detection of small amounts of numerous glycans at a time. Tools that allow researchers to study glycosylation of the proteome (the entire complement of proteins that is or can be expressed by a cell, tissue, or organism) – or “glycoproteome” – will accelerate our understanding of glycosylation in disease and facilitate the development of therapeutic targets to treat disease.
To address this challenge, Common Fund Glycoscience grantee, Dr. Carolyn Bertozzi, and researchers applied a recently developed method to analyze the glycoproteomes from a collection of diverse human cell lines. IsoTaG, a method previously developed by this group, uses the cell’s metabolism to label sugars in distinct patterns and identify glycosylation modifications. Unlike existing methods that can rely on abundance of a glycosylated protein, IsoTag improves the detection of low abundance glycosylation modifications through the use of metabolic labeling to generate unique signatures and applies computation to recognize these signatures. In a new study, Dr. Bertozzi and researchers applied the IsoTaG method to 15 human cell lines, including those from the brain, liver, kidney, and breast. This study identified over 3500 glycopeptides, which contained 74 unique glycan structures, all provided on a web-based platform for public access (www.isostamp.org). These results provide the foundation for enhancing our understanding of glycosylation in the context of the whole cell proteome and may help researchers understand the role of glycosylation in a range of biological processes.
Reference: Development of IsoTaG, a Chemical Glycoproteomics Technique for Profiling Intact N- and O-Glycopeptides from Whole Cell Proteomes. Woo CM, Felix A, Byrd WE, Zuegel DK, Ishihara M, Azadi P, Iavarone AT, Pitteri SJ, Bertozzi CR. Journal of Proteome Research. 2017 February 28.
Common Fund Glycoscience grantee Dr. Eric Jacobsen and collaborators at Harvard University have developed a new approach to allow more scientists to study important biological sugar molecules, advancing research and accelerating progress in understanding the role of sugars in human health and disease. Carbohydrates, or sugars, are naturally occurring chemical compounds present throughout every living cell. Although carbohydrates play key roles in several biological processes, including photosynthesis and metabolism, they have remained largely understudied because generating carbohydrates in a laboratory is challenging. Carbohydrates are generated through chemical synthesis, the construction of complex chemical compounds from simpler ones. Due to their complicated three dimensional structure, or stereochemistry, carbohydrates are especially complex compounds, which makes their chemical synthesis difficult and erratic.
To overcome this challenge, Dr. Jacobsen and collaborators developed a method to generate complex carbohydrates in a stereospecific manner using a unique chemical catalyst. A catalyst is a substance that enables a chemical reaction to proceed at a faster rate or under different conditions than otherwise possible. For example, a glycosylation enzyme is a biological catalyst that attaches carbohydrates to other molecules in living cells. Interestingly, the chemical catalyst developed by Dr. Jacobsen’s group mimics biological glycosylation enzymes. Using a chemical catalyst instead of enzymatic catalyst can be useful when large amounts of carbohydrate are required for research. This is because biological enzyme catalysts may be unstable or hard to isolate. Additionally, although there are existing enzymes and methods to synthesize carbohydrates, these approaches are not predictable or straight forward. This means that every time a scientist wants to synthesize a carbohydrate to study it, the expertise of a carbohydrate synthesis specialist is required. This new approach has the potential to enable the study of glycoscience by non-specialists, a major goal of the Common Fund’s Glycoscience program and an important step in advancing the field of glycoscience.
In the news: Sweeter hookups between sugars using a macrocyclic catalyst
Glycans, or sugars, are attached to many cellular proteins and play important roles in a variety of cellular processes. All cells carry an array of glycans that modulate molecules that are critical to the development and function of multicellular organisms. Additionally, the glycans present on cellular proteins change with disease state, making glycans useful as disease biomarkers (a measurable substance in an organism whose presence is indicative of disease, infection, or environmental exposure). However, analysis of glycans in clinical specimens is limited because current methods tend to require higher concentrations of glycan than is typically available from a clinical specimen. To overcome this challenge, Common Fund Glycoscience Program grantee Dr. Brian Haab and collaborators have developed a new method that allows for the detection of small sample of human plasma (the clear, liquid part of the blood, composed mainly of water and proteins, in which the blood cells are suspended), as well as precision comparisons over multiple samples. Using this new method, called on-chip glycan modification and probing (on-chip GMAP), proteins with glycan modifications were immobilized on a surface and the amount of glycans on the proteins was detected. They precisely analyzed glycans found on proteins, as well as compared the presence and structure of glycans over multiple samples and disease states. As a proof of principle, on-chip GMAP was used to detect the cancer biomarker MUC5AC, a glycoprotein extracted from human plasma. The amount of protein required was 25 – 50 times lower than previous methods. This new method can be used as a platform for analyzing small amounts of a given glycoprotein in clinical specimens and determining how these glycoproteins change in disease.Reference: Characterizing Protein Glycosylation through On-Chip Glycan Modification and Probing. Reatini BS, Ensink E, Liau B, Sinha JY, Powers TW, Partyka K, Bern M, Brand RE, Rudd PM, Kletter D, Drake RR, Haab BB. Analytical Chemistry. 2016 Nov 3
Given the complexity of carbohydrates, their use in biological studies requires that they be of the highest level of purity to ensure rigorous and reproducible results in biological experiments. Inadequate access to pure carbohydrates has long hindered the study of their biology and impact on human health, as well as their therapeutic value. To address roadblocks in carbohydrate purification, Glycoscience grantees Drs. Nicola Pohl and Milos Novotny, from Indiana University, have developed a new protocol for the purification of carbohydrates. This low cost methodology addresses biologists concerns for access to glycans of greater than 99% purity.Reference: Protocol for the purification of protected carbohydrates: toward coupling automated synthesis to alternate-pump recycling high-performance liquid chromatography.Chemical Communications. 2016 October 24.
Novel Tool for Quantitative Detection of O-GlcNAc Modifications on Specific Proteins.
Proteins are large biomolecules that are required for the structure and function of the body’s cells and tissues. The human body contains somewhere between 17 to 18 thousand different proteins. The function of any one of these proteins can be changed by the addition or removal of chemical modifications to the protein. These modifications can exert profound effects on a proteins activity, cellular localization, and/or its interaction with other proteins and biomolecules. O-GlcNAcylation is a protein modification that has been implicated in multiple disease process including cancer, diabetes, and Alzheimer’s disease. However, O-GlcNAcylation of proteins can only be currently analyzed using complicated procedures that are accessible to just a few scientists who have highly specialized and expensive equipment. To overcome these hurdles, Common Fund Glycoscience grantee Dr. Carolyn Bertozzi has developed a new method, termed Glyco-seek. Taking advantage of a common laboratory method (polymerase chain reaction, PCR), Glyco-seek is more convenient than existing methods for the detection of O-GlcNAcylated proteins. In addition to being more amenable to most research laboratories, Glyco-seek also shows ultrahigh sensitivity when compared to current techniques. This method has potentially broad applications for the study of other forms of glycosylation, as well as the potential to enable the broader scientific community to easily analyze glycosylated proteins.Reference: Glyco-seek: Ultrasensitive Detection of Protein-Specific Glycosylation by Proximity Ligation PCR. Journal of the American Chemical Society. 2016 July 25.
Glycomics is the study of all glycan structures of a given cell type or organism. Rigorous examination of any given glycome requires the efficient release, recovery, and analysis of all glycans from that cell type or organism. Subsequent study of individual glycans further requires they be available in sufficient quantity and that methods and standards for their identification be available. The chemical and enzymatic synthesis of thousands of naturally occurring glycans is a significant challenge in the field of glycomics. Toward overcoming this challenge, Glycoscience Program awardees Drs. Xuezheng Song and Richard Cummings have developed a new facile strategy for obtaining naturally occurring glycans from biological tissues, including mouse and pig. Traditional methods for preparing natural glycans are both lengthy and expensive. Further, they rely on enzymatic digestions that typically produce limited quantities of glycans (milligrams). To overcome these obstacles, Drs Song and Cummings have developed a new strategy, called oxidative release of natural glycans (ORNG), which quickly releases glycans from biological samples (both proteins and lipids) in kilograms quantities, alleviating the need for expensive enzymes and prolonged digestion times. This new and innovative approach is a significant step forward because it uses an inexpensive and mild reagent (household bleach) to “substantially improve the simplicity and accessibility” of mammalian glycomes, allows further study of their functions, and provides them in significant quantity for development of tools.
In the news: Read more about Dr. Richard Cummings and the ORNG approach here.
Reference: Oxidative release of natural glycans for functional glycomics. Song X, Ju H, Lasanajak Y, Kudelka MR, Smith DF, Cummings RD. Nature Methods 2016 June 13.
This page last reviewed on May 4, 2017