Scientific insights from studying the genetic code have revealed significant information regarding the cellular building blocks of proteins and lipids. While extensive, the information is not sufficient to explain the diverse structures and functions of these cellular components. As it turns out, these molecules are decorated with covalently attached complex layers of sugars, giving rise to millions of possible structures. The resulting glycoconjugates are the main actors behind protein folding and stability, facilitating essential cellular processes and communication. In essence, glycobiology studies the structure and function of these sugar chains, their conjugates, and their impact on health, disease, and evolution.
Thanks to the thriving field of glycobiology, we are learning more about the importance of glycans as they relate to biological processes in our bodies. More importantly, we are learning how we can leverage glycans for various biotechnology applications to design cutting-edge therapeutics.
Keep reading for insights in glycobiology’s role in diagnostics, therapeutics, and stem cell research, and if you’re interested in knowing more about the growing field of glycobiology, check out our Glycobiology Resources page.
Aberrant glycosylation, which is abnormalities in the conjugation between sugars and proteins or lipids, is a clear indicator of disease. Researchers can leverage assays such as chromatography, lectin arrays, and flow cytometry to identify and quantify different glycan structures in healthy and diseased tissues. Furthermore, immunohistochemistry and immunofluorescence methods allow us to monitor the effect of aberrant glycosylation on cell morphology and movement. The combination of these glycan detection tools have provided invaluable insights into the nature of several diseases, including congenital disorders, diabetes, cancer, and COVID-19.
Today, over 100 congenital diseases have been attributed to altered glycosylation networks, mainly the overexpression of certain N-glycans over others (1). While some of these diseases might be inherited from parents carrying the genes, others might develop due to random mutations in the glycosylation networks. Examples include hypotonia (poor muscle tone), ataxia (impaired balance and coordination), cardiomyopathy (insufficient blood pumped from the heart), dysarthria (slurred speech), liver dysfunction, excessive blood clotting, and scoliosis, all of which severely affect the individual’s quality of life from the moment they are born.
Dysregulated glycosylation has also been explored in cancer and is now a widely accepted cancer biomarker. The post-translational modifications in proteins help identify cancerous tissues and indicate aggression, malignancy, and metastatic behavior. Today, many FDA-approved cancer biomarkers are glycoproteins for cancers such as ovarian (2), pancreatic (3), and breast (4). While some studies have identified single glycoproteins, others have discovered a panel of glycoproteins affecting cancer progression, such as in head and neck cancers (5).
Epidemiology is another field where the role of glycosylation is being investigated. Researchers have observed that pathogens attack and enter our cells due to their diverse surface glycans. There are many examples of this, but perhaps the most relevant is how SARS-CoV-2 uses its spike glycoprotein to attach and enter host cells (6).
Many small molecule drugs have glycans in their natural core structures. With the expanding knowledge about glycosylation mechanisms, investigators have started to modify these glycans to improve the efficacy of protein-based therapeutics.
Zanamivir (Relenza) or Oseltamivir (Tamiflu) for influenza treatment are among the most well-known examples. Adding glycosylated side chains to the original drug molecules increased their inhibition of virus binding without cytotoxicity to the host cell (7). In one of the pioneering studies, IgG antibodies with fucosylated N-glycans bound natural killer cells 50 times tighter than standard IgGs, making them more effective in activating natural killer cells (8).
In recent years, glycobiology has become increasingly significant in creating engineered microorganisms that mass produce therapeutic glycoproteins (9). Through recombinant DNA technology, researchers can insert glycosyltransferase genes into widely-studied organisms like E. coli to express glycoproteins.
Another emerging application of glycobiology is the synthesis of glycoprotein vaccines. Although glycan chains were previously used as vaccine candidates, they exhibited poor immunogenicity and failed to activate T-cells. As a result, researchers shifted gears to synthesize vaccines in glycoconjugate forms to increase long-term B-cell memory. Such vaccines comprise a glycan antigen (usually O-antigen polysaccharides), a conjugate (protein), and an adjuvant molecule to enhance immunogenicity.
Since 1980, several antibacterial glycoconjugate vaccines have received approval from the FDA. These vaccines have been shown to protect infants against various bacterial infections, including Hemophilus influenzae type B, Streptococcus pneumoniae, and Neisseria meningitis (10).
Current research emphasizes the rapid and cost-effective production of glycoconjugates through engineered microorganisms, mainly E. coli. While the cellular machinery of E. coli strains lacks the post-translational modification mechanism, recombinant DNA technologies can be used to grant them the ability to do so. Preliminary studies have transferred glycosyltransferase genes from eukaryotes into E. coli to produce glycoconjugates against several pathogenic strains (11).
More recently, glycoconjugate vaccines have started to attract attention in cancer research. Attempts to develop anticancer vaccines primarily focus on training the immune system to attack tumor-associated carbohydrate antigens (TACAs). Extensive research is being performed particularly in vaccines against gangliosides and mucin-type glycoproteins, both identified as biomarkers for several cancer types, including prostate, colon, lung, and ovarian (12).
Functional nanomaterials, such as iron oxide, quantum dots, and carbon nanotubes, are on the rise due to their potential for targeted drug delivery and their ability to infiltrate otherwise inaccessible tissue parts. These nanomaterials are optimized through chemical processes, such as conjugation, to perform specific tasks (e.g., fluorescence imaging and targeted drug delivery) while remaining compatible with the human body. Combining these materials with glycan-based therapeutics can bring glycoconjugates smart features that they would not harbor in their natural states (13).
For example, researchers have used the self-assembly capacity of nanomaterials to synthesize self-assembling glycopeptides that formed nanofibers. Preliminary research demonstrated the effectiveness of these nanofibers as galectin inhibitors, indicating their potential against cancer, inflammation, and viral diseases (14). Other preliminary studies have involved the development of self-adjuvant MUC1 vaccines which elicit a more effective immune response against MUC1-associated tumors (15).
A significant portion of embryonic development involves the differentiation of stem cells into different cell types which form our neurons, skin, and organs. ￼Research shows that surface glycoproteins and glycolipids, especially their terminal sialic acids, are the key triggers of stem cell differentiation. Furthermore, the glycan profile has been found to undergo modifications several times throughout the differentiation. In other words, the glycan profile of stem cells could predict their state and type of differentiation. There appears to be a bidirectional relationship between stem cell differentiation and glycosylation that might shed light on the mysteries of developmental biology (16).
Stem cell research can give rise to groundbreaking cell replacement therapies, enabling repair or replacement of damaged tissues and organs. From this point of view, a robust understanding of glycosylation during stem cell differentiation can greatly benefit regenerative medicine.
Today, immense effort is put into developing stem cell therapies for many neurological diseases, such as Parkinson’s disease, as glycobiology research has massive potential for generating differentiated neural cell lines (17). There is also potential for glycobiology research to improve our portfolio for cancer stem cell biomarkers. It is now known that cancer stem cells are pivotal in tumor initiation and metastasis (18). Exploring the glycan profiles of this subset of cells can help scientists develop more robust therapeutics against cancer stem cells and reduce the risk of anticancer drug resistance.
The sugar chains on the cell surface are highly diverse with millions of possible structures, so it is an everlasting mission to discover the vast ocean of carbohydrates. Nevertheless, substantial progress is being made in many research fields to understand our origins and improve our quality of life.
Could glycobiological tools help you unravel your scientific questions? If this article left you curious, head on over to our Lectins & Glycobiology Reagents page or download our new eBook, Exploring the World of Glycobiology, to learn how Vector Laboratories can support your own research on these super sugars.