Glycosylation

Extracted Attributes

• Main Classes

  N-linked, O-linked, Phosphoglycans, C-linked, Glypiation

• Process Type

  Enzyme-catalyzed reaction

• Primary Locations

  Rough endoplasmic reticulum, Golgi apparatus, cytoplasm, nucleus

• Biological Functions

  Protein folding, stability, cell-to-cell adhesion, immune recognition

• Modification Category

  Co-translational and post-translational modification

• Therapeutic Application

  Inverse vaccine for autoimmune disease retraining

Timeline

• Glycosylation occurs naturally as a co-translational and post-translational modification in eukaryotic cells. (Source: Wikipedia)

  Ongoing

• David Friedberg discusses a Nature paper where University of Chicago researchers used glycosylation to halt Type 1 Diabetes and Multiple Sclerosis in animal models. (Source: Document 0ec8558c-54ac-4c28-a128-3d525017e6c2)

  2023-09-22

Glycosylation

Glycosylation is the reaction in which a carbohydrate (or 'glycan'), i.e. a glycosyl donor, is attached to a hydroxyl or other functional group of another molecule (a glycosyl acceptor) in order to form a glycoconjugate. In biology (but not always in chemistry), glycosylation usually refers to an enzyme-catalysed reaction, whereas glycation (also 'non-enzymatic glycation' and 'non-enzymatic glycosylation') may refer to a non-enzymatic reaction. Glycosylation is a form of co-translational and post-translational modification. Glycans serve a variety of structural and functional roles in membrane and secreted proteins. The majority of proteins synthesized in the rough endoplasmic reticulum undergo glycosylation. Glycosylation is also present in the cytoplasm and nucleus as the O-GlcNAc modification. Aglycosylation is a feature of engineered antibodies to bypass glycosylation. Five classes of glycans are produced: N-linked glycans attached to a nitrogen of asparagine or arginine side-chains. N-linked glycosylation requires participation of a special lipid called dolichol phosphate. O-linked glycans attached to the hydroxyl oxygen of serine, threonine, tyrosine, hydroxylysine, or hydroxyproline side-chains, or to oxygens on lipids such as ceramide. Phosphoglycans linked through the phosphate of a phosphoserine. C-linked glycans, a rare form of glycosylation where a sugar is added to a carbon on a tryptophan side-chain. Aloin is one of the few naturally occurring substances. Glypiation, which is the addition of a GPI anchor that links proteins to lipids through glycan linkages.

Web Search Results

• Glycosylation - Wikipedia

  Biochemical process Not to be confused with Glycation. See also: Chemical glycosylation Glycosylation is the reaction in which a carbohydrate (or 'glycan'), i.e. a glycosyl donor, is attached to a hydroxyl or other functional group of another molecule (a glycosyl acceptor) in order to form a glycoconjugate. In biology (but not always in chemistry), glycosylation usually refers to an enzyme-catalysed reaction, whereas glycation (also 'non-enzymatic glycation' and 'non-enzymatic glycosylation') may refer to a non-enzymatic reaction. [...] Glycosylation is the process by which a carbohydrate is covalently attached to a target macromolecule, typically proteins and lipids. This modification serves various functions. For instance, some proteins do not fold correctly unless they are glycosylated. In other cases, proteins are not stable unless they contain oligosaccharides linked at the amide nitrogen of certain asparagine residues. The influence of glycosylation on the folding and stability of glycoprotein is twofold. Firstly, the highly soluble glycans may have a direct physicochemical stabilisation effect. Secondly, N-linked glycans mediate a critical quality control check point in glycoprotein folding in the endoplasmic reticulum. Glycosylation also plays a role in cell-to-cell adhesion (a mechanism employed by cells of the [...] Glycosylation is a form of co-translational and post-translational modification. Glycans serve a variety of structural and functional roles in membrane and secreted proteins. The majority of proteins synthesized in the rough endoplasmic reticulum undergo glycosylation. Glycosylation is also present in the cytoplasm and nucleus as the O-GlcNAc modification. Aglycosylation is a feature of engineered antibodies to bypass glycosylation. Five classes of glycans are produced:

• Glycosylation | Thermo Fisher Scientific - US

  Glycosylation, the attachment of sugar moieties to proteins, is a post-translational modification (PTM) that provides greater proteomic diversity than other PTMs. Glycosylation is critical for a wide range of biological processes, including cell attachment to the extracellular matrix and protein–ligand interactions in the cell. This PTM is characterized by various glycosidic linkages, including N-, O- and C-linked glycosylation, glypiation (GPI anchor attachment), and phosphoglycosylation. Glycoproteins can be detected, purified and analyzed by different strategies, including glycan staining and visualization, glycan crosslinking to agarose or magnetic resin for labeling or purification, or proteomic analysis by mass spectrometry, respectively. ### Page contents [...] Glycosylation is thought to be the most complex post-translational modification because of the large number of enzymatic steps involved (5). The molecular events of glycosylation include linking monosaccharides together, transferring sugars from one substrate to another and trimming sugars from the glycan structure. Unlike other cell processes such as transcription or translation, glycosylation is non-templated, and thus, all of these steps do not necessarily occur during every glycosylation event. Instead of using templates, cells rely on a host of enzymes that add or remove sugars from one molecule to another to generate the diverse glycoproteins seen in a given cell. While it may seem chaotic because of all of the enzymes involved, the different mechanisms of glycosylation are [...] ### Glycan attachment Glycosylation is often characterized as a post-translational modification. While this is true with other types of glycosylation, N-glycosylation often occurs co-translationally, in that the glycan is attached to the nascent protein as it is being translated and transported into the ER. The "N" in the name of this type of glycosylation denotes that the glycans are covalently bound to the carboxamido nitrogen on asparagine (Asn or N) residues.

• Effect of glycosylation on protein folding: From biological roles to ...

  Glycosylation, a prevalent post-translational modification (PTM) across eukaryotic systems, plays a pivotal role in protein folding, stability, and functionality.36,37,38 This review specifically focuses on the role of glycosylation in biotechnology applications, emphasizing its utility in enhancing the solubility, stability, and folding of proteins during biomanufacturing. The process is predominantly discussed within the context of eukaryotic glycoproteins, encompassing yeast and mammalian systems, which represent the most commonly utilized models for studying glycosylation dynamics and applications in protein synthesis. [...] Chemical protein synthesis has become an important tool in biotechnology and synthetic biology for producing proteins with complex structures. However, achieving correct folding in vitro remains a significant challenge. Glycosylation, a ubiquitous modification, stabilizes folding intermediates, prevents aggregation, and accelerates folding in both cellular and cell-free systems. In this review, we discuss the dual role of glycosylation in biological systems and in vitro experiments, focusing on how it promotes protein folding and stability. We also discuss the temporary glycosylation scaffold strategy for chemical protein synthesis, which offers a reversible approach to guide protein folding without leaving permanent modifications. This strategy provides a promising solution to the [...] ## Conclusion and perspective Glycosylation plays an essential role in protein folding, stability, and maturation within biological systems. In natural settings, glycosylation facilitates protein folding by stabilizing intermediates, preventing aggregation, and supporting quality control mechanisms within the endoplasmic reticulum (ER). However, for chemically synthesized proteins, the absence of these natural folding pathways presents considerable challenges, particularly when dealing with complex proteins containing multiple disulfide bonds or large tertiary structures. These limitations frequently lead to misfolding and reduced yields.

• Glycosylation: mechanisms, biological functions and clinical ... - Nature

  Protein is essential for life and involved in all cellular processes. Proteins undergo dynamic changes and various PTMs such as phosphorylation, methylation, acetylation, and notably glycosylation.8.") Glycosylation, being one of the known PTMs, is essential in the unfolding of various functional activities in living organisms.9.") Glycosylation of proteins is the process of covalently binding oligosaccharides in the form of glycosides to certain amino acid residues on proteins.10.") The amino acids and glycans are classified into four categories according to their linkage: O-glycosylation, N-glycosylation, C-glycosylation and GPI-anchored attachment10."),11.") (Fig. 2). Among them, N-glycosylation and O-glycosylation are the most common types and they contain most glycosylation machinery [...] O-glycosylation is generally an oxygen linkage of glycans to the Ser or Thr residues, followed by a gradual addition of monosaccharides. Unlike N-glycosylation, which generally occurs in the ER and Golgi apparatus, O-glycosylation occurs mainly in the nucleus and cytoplasm.21.") The two most common types of O-linked glycosylation are O-acetylgalactosamine (O-GalNAc) and O-linked-β-D-N-acetylglucosamine (O-GlcNAc).22 117–128 (2022).") O-GalNAc glycosylation is initiated by polypeptide N-acetylgalactosaminyl-transferase, GalNAc monosaccharides are attached to Ser or Thr residues of proteins by O-glycosidic bonds.23."),24.") This dense O-GalNAc glycosylation, also known as O-glycosylation mucins, is expressed in a variety of tumor types and plays a role in cell-cell interaction, and [...] Abnormal glycosylation in breast cancer impacts cell signaling, adhesion, and immune recognition, contributing to the cancer’s aggressiveness.6."),255.") Moreover, aberrant glycosylation enables breast cancer cells to evade immune detection, facilitating tumor progression.181."),256.") Current biomarkers for breast cancer prognosis and treatment still lack applicability and precision. Glycosylation patterns in breast cancer are potential biomarkers for early diagnosis, prognosis, and treatment monitoring, with unique glycan structures identified in breast cancer cells.257.") Targeted therapies aiming at these altered glycosylation pathways, such as inhibiting specific glycosylation enzymes, show promise in reducing tumor growth and enhancing treatment efficacy. Furthermore, research

• The Basics of Protein and Antibody Glycosylation - Rapid Novor

  The compartmentalized nature of protein glycosylation gives rise to a wide range of glycoproteins with diverse structures, leading to unique glycan profiles that reflect distinct protein functions. ## Why are Proteins Glycosylated? The vast diversity of glycans introduces an additional layer of complexity to the proteome, significantly influencing cellular function down to individual protein activity. At the protein level, glycosylation functions to: 1. Promote proper protein folding by enhancing thermal and kinetic stability and reducing the free energy of protein folding. 2. Enhances protein stability by stabilizing existing conformations, preventing thermal unfolding, and inhibiting degradation by proteases. At the cellular level, glycosylation functions in various ways: [...] The process begins with the synthesis and translation of a protein in the ER, where the initial stages of protein folding occur. Following translation, glycans are enzymatically attached to amino acid residues, predominantly asparagine (N-linked glycosylation) or serine and threonine residues (O-linked glycosylation). In the Golgi, glycosylated proteins undergo additional modifications, facilitated by various enzymes and protein chaperones which trim or elongate glycans. Although O-linked glycosylation can commence in the ER, it predominantly initiates in the Golgi apparatus after the completion of protein folding. [...] ### Fc Region Antibody Glycosylation In the fragment crystalline (Fc) region of antibodies, glycosylation occurs at the highly conserved residue, Asn 297, in all human IgG molecules (Figure 2). Buried between the Fc-domains, glycan modifications can modulate effector functions, such as antibody-dependent cellular cytotoxicity (ADCC) and complement activation. Although glycosylation of Asn 297 is conserved, there is significant heterogeneity in IgG glycan modifications. Modifications to the core glycan influences interactions with Fc gamma receptors (FcγR), thereby impacting the recruitment and activity of immune effector cells. Additionally, Fc N-glycosylation has also been shown to improve antibody stability and half-life, and reduce the aggregation propensity of antibodies.