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The Secret of Sugar: Why Are Glycans So Important in Cells?
In the world of molecular biology, the role of sugar molecules is often underestimated. Most people only view sugar in their diet as a source of energy or a sweetener. However, when we delve deeper into the mechanisms of the cell, we find that the building blocks of sugar, glycans, play an extremely important role. These molecules, composed of multiple sugar units, not only affect the structure and function of cells, but also play an indispensable role in many biological processes.
Glycans are polymers composed of monosaccharides linked by glycosidic bonds, usually composed of O- or N-linked sugar chains.
Glycans have diverse structures, including homo- and hetero- oligosaccharides, and even linear or branched structures. They are usually located on the cell surface, interacting with the extracellular environment and other cells. The most common types of glycans are divided into two categories: N-linked glycans and O-linked glycans. Each type plays a different role in the physiological function of the cell, especially in protein folding, cell signaling and immune response.
Key Role: N-Glycans
N-linked sugars are formed by linking to the nitrogen atom of asparagine amino acid. This process occurs in the endoplasmic reticulum. The core structure of Glycan is composed of 14 monosaccharides, including 3 glucoses, 9 mannoses, and 2 N-acetyl glucosamines.
N-linked sugars not only play an important role in the correct folding of proteins, but are also crucial for cell signaling and the function of the immune system.
Once an N-linked sugar is attached to a nascent peptide chain, the structure typically undergoes a series of processing reactions that involve the removal of multiple sugar units, especially glucose. The modification and expression of this sugar is crucial in the proper functioning of cells, especially in regulating the cell's immune response. For example, abnormal Glycans expressed on the surface of tumor cells are recognized by natural killer cells, indicating that the cell may be cancerous.
Composition and function of O-linked sugars
Compared with N-linked sugars, the synthesis process of O-linked sugars is to add monosaccharides one by one. This process takes place in a high matrix, opening up the possibility of flexible structures that are thought to play important roles in regulating cell-cell interactions. O-linked sugars in particular play important roles in blood antigen recognition and immune responses; for example, the Sialyl Lewis X (SLex) structure plays a role in the migration of neutrophils.O-linked sugars act like flags on the surface of the immune system, allowing immune cells to precisely enter the appropriate tissue to respond to infection.
Compared to N-linked sugars, the sequences of O-linked sugars are more random, which makes them more functional and diverse in cells. O-linked sugars are also contained in a large number of mucins, which are essential for the formation of intestinal microbiota and the maintenance of normal intestinal microbial flora.
Glycosaminoglycans and extracellular matrix
Another important carbohydrate molecule is glycosaminoglycans (GAGs), a special class of polymers that are generally composed of alternating links of amino sugars and uric acid. GAGs, such as heparin and chondroitin, are primarily found in the extracellular matrix, where they contribute to structural support and interactions between cells. These sugar molecules also play an important role in cell signal transduction processes.
Future trends: Glycoscience
Despite the increasing recognition of their importance in cellular function, glycans have often been overlooked in past studies. Many researchers are advancing glycoscience, a field focused on the structure and function of glycans, which is expected to bring breakthrough advances in a variety of fields, including medicine, energy generation, and materials science.
The development of glycoscience can not only reveal the basic laws of life, but also has the potential to revolutionize our understanding and treatment of diseases.
In the study of glycans, we have seen innovations in technologies such as high-resolution mass analysis and high-performance liquid chromatography, which have enabled researchers to more accurately detect the structure and properties of sugars. Since 2012, many countries have begun to pay attention to glycoscience and expand its application in research.
So, what unexpected insights can Glycans bring us when it comes to understanding the complexity of cells?
