The Development of Improved Therapeutics through a Glycan- “Designer” Approach
Peter Grunwald in Pharmaceutical Biocatalysis, 2019
O-linked glycosylation on the contrary is a dynamically explored field due to its potent role in mammalian pathophysiological processes. O-linked glycosylation is characterized by a covalent attachment of glycan through an oxygen atom. The O-linked consensus is initiated by an attachment of N-Acetylgalactosamine (GalNAc) to Ser/Thre but may also be composed of O-linked β-N-acetylglucosamine; hence, classification of O-glycans is according to their initiating monosaccharide. There are around five classes of O-glycosyl modifications known in mammalian cells, these are: O-N-acetylgalactosamine, O-fucose, O-glucose, O-N -acetylglucosamine and O-mannose. Oligosaccharide attachment is catalyzed by O-glycosyltransferases (OGTs) upon recognition of the Asn-X-Ser/Thr (where X is any amino acid). There are many bacterial glycosyltransferases already employed for in vitro controlled glycosylation, opening very successful field of protein glycoengineering. The glycan polymer may vary in heterogeneity, which makes the prediction of monosaccharide building blocks variable in vivo. Additionally, the extra branching of O-glycans involves multiple glycosyltransferases.
Multiple Roles of Cardiac Metabolism: New Opportunities for Imaging the Physiology of the Heart
Robert J. Gropler, David K. Glover, Albert J. Sinusas, Heinrich Taegtmeyer in Cardiovascular Molecular Imaging, 2007
In preliminary experiments, we observed that altered glucose homeostasis through feeding of an isocaloric low carbohydrate, high fat diet completely abolishes MHC isoform switching in the hypertrophied heart (32). One mechanism by which glucose affects gene expression is through O-linked glycosylation of transcription factors. Glutamine, fructose-6-phosphate amidotransferase (gfat) catalyzes the flux-generating step in UDP-N-acetylglucosamine biosynthesis, the rate determining metabolite in protein glycosylation (Fig. 7). In preliminary studies, we observed that overload increases the intracellular levels of UDP-N-acetylglucosamine (unpublished work in collaboration with Dr. Don McClain, University of Utah). Thus, there is early evidence for glucose-regulated gene expression in the heart and, more specifically, for the involvement of glucose metabolites in isoform switching of sarcomeric proteins. More importantly, excess O-GlcNAcylation in the diabetic heart appears to play a significant role in cardiac function because reducing this excess cellular O-GlcNAcylation improves calcium handling and cardiac contraction in diabetic mice (63).
Postimplantation diabetic embryopathy
Moshe Hod, Lois G. Jovanovic, Gian Carlo Di Renzo, Alberto de Leiva, Oded Langer in Textbook of Diabetes and Pregnancy, 2018
Under normoglycemic conditions, approximately 1%–3% of total glucose consumed by somatic cells is directed down the hexosamine pathway.278 UDP-GlcNAc is the substrate for the majority of glycosylation in the cell, producing mucopolysaccharides.279 In this process, UDP-GlcNAc is attached to serine or threonine residues of proteins, thus becoming a posttranslational modification (beta-O-linked glycosylation), which regulates protein function in an analogous manner to phosphorylation.280 Altered beta-O-linked glycosylation has been associated with a number of disease states, including cancer, inflammatory conditions, and neurodegenerative diseases.281 Notably, it is also implicated as a primary mechanism behind the development of insulin resistance and pancreatic beta-cell destruction in type 2 diabetes.278,281
Human carbonic anhydrases and post-translational modifications: a hidden world possibly affecting protein properties and functions
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2020
Anna Di Fiore, Claudiu T. Supuran, Andrea Scaloni, Giuseppina De Simone
Protein O-linked glycosylation is a PTM that involves the chemical linkage of a mono-/polysaccharide molecule to the oxygen atom of S/T residues82. In eukaryotes, it occurs after the protein has been synthesised, and generally takes place in the endoplasmic reticulum (ER) and Golgi apparatus. Different sugars can be introduced in the protein structure; based on their nature, they can affect the protein properties in different ways by changing corresponding stability and regulating activity. O-linked glycans have various physiological functions, such as regulation of cell trafficking in the immune system, recognition of foreign material, control of cell metabolism and provision of cartilage and tendon flexibility. Because of the many functions they have, changes in O-glycosylation are important in many diseases including cancer, diabetes and Alzheimer’s.
Employing proteomics in the study of antigen presentation: an update
Published in Expert Review of Proteomics, 2018
Sri H. Ramarathinam, Nathan P. Croft, Patricia T. Illing, Pouya Faridi, Anthony W. Purcell
Glycosylation of proteins involves the addition of carbohydrate molecules to amino acids – mostly N- or O-linked glycosylation on N or S/T, respectively. Proteins in eukaryotic cells undergo extensive glycosylation in the endoplasmic reticulum and Golgi complexes with the participation of numerous enzymes that impact localization, protein stability, surface expression and secretion [63]. This presents unique challenges in identification due to the heterogeneity of the glycans (including varying branch and chain lengths) on proteins often resulting in multiple isoforms. Current strategies include enzymatic deglycosylation (EndoH, PNGase-F) in addition to specific enrichment, derivatisation, or manual sequencing [64,65]. Of note, removal of N-glycans using PNGase-F results in the conversion of N to D (resulting in a mass difference of 0.98, i.e. that of deamidation of N as described above). One of the earliest known glycopeptides was described by Engelhard et al. where a HLA-A*02:01 restricted peptide YMD*GTMSQV(N3-glyco to D) was identified using mass spectrometry [66]. Only a handful of studies have identified glycopeptides since, and most of them required manual identification of mass spectra highlighting the challenges involved [67–70].
Glycosylation and its implications in breast cancer
Published in Expert Review of Proteomics, 2019
Danielle A. Scott, Richard R. Drake
Alterations in breast cancer mucin-type O-linked glycosylation can result in tumor growth and progression through a variety of mechanisms. In the immune system, changes in mucin-type O-linked glycosylation can produce novel interactions between immune cells and lectins. This is demonstrated through the binding of sialylated glycans to sialic acid-binding immunoglobulin-type lectins (siglecs) on monocytes, macrophages, and NK cells. Examples of this specific mechanism include the binding of sialylated MUC1 to siglec-9 on monocytes and macrophages, the binding of sialylated LacNAc (found on core 1 or core 2 branches) to siglecs-7 on NK cells, and the binding of Tn and sialylated Tn antigens to macrophage galactose-specific lectin on dendritic cells and macrophages. Furthermore, the expression of sialyl Lewisx can result binding to selectins on endothelial cells and various core glycans which can dictate how the cancer cells metastasize and respond to epidermal growth factor (EGF) binding [58,88,100–102]. Sialyl Lewisx antigens on leukocytes can contribute to inflammatory response as a result of their interaction with E-selectin on endothelial cells. Interactions between selectins and sialyl Lewisx glycans are crucial for immune cell trafficking, indicating that the cancer is exploiting a normal cellular process to aid in metastasis [58,102]. This interaction exposes sialyl Lewisx antigens at the cell surface, a mechanism that malignant cells capitalize upon for extravasation from the blood circulation and metastasis [103].
Related Knowledge Centers
- Cytoplasm
- Eukaryote
- Golgi Apparatus
- Oxygen
- Prokaryote
- Threonine
- Serine
- Sugar
- Post-Translational Modification
- Endoplasmic Reticulum