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From cell surface to interior: How do N-Linked Glycans affect protein folding?
The functions of Glycans are often overlooked among biomolecules, but they are crucial to the basic functioning of cells. Especially in the protein folding process, N-Linked glycans demonstrate their indispensable role. This process not only affects the shape of proteins inside cells, but is also related to the normal operation of many biological functions.
N-Linked Glycans are carbohydrate structures linked to the amino acid asparagine (Asn). This structure is synthesized in the endoplasmic reticulum and is part of protein biosynthesis.
Structure and function of N-Linked Glycans
The synthesis of N-Linked glycans begins in the endoplasmic reticulum when two N-acetylglucosamines combine with dolichol monophosphate. Five mannose residues were then added to the structure, resulting in a core structure of 14 monosaccharide residues. These 14 residues include 3 glucose, 9 mannose, and 2 N-acetylglucosamine.
These 17 different groups not only determine the structure of N-Linked glycans, but also affect their subsequent contribution to protein folding.
Once N-Linked glycans are transferred to a newly synthesized polypeptide chain, they undergo a series of processes in which sugar residues are removed based on specific protein folding requirements. For example, the removal of glucose residues depends on the protein folding correctly; if folding fails, these glucoses will reattach to the protein and recombine with molecular chaperones.
Regulation of protein folding
N-Linked glycans are essential for the correct folding of proteins. Chaperone proteins in the endoplasmic reticulum, such as calnexin and calreticulin, bind to glucose residues on N-Linked glycans and help newly synthesized polypeptides fold into the correct structure.
If a protein cannot reach the correct shape after repeated folding processes, it will eventually be expelled from the endoplasmic reticulum and degraded by intracellular proteases.
In addition, the presence of N-Linked glycans can also affect the internal structure of proteins, temporarily preventing cysteine from forming disulfide bonds through steric effects, so that cells can better control the disulfide bond formation process in low energy states. .
The role of cell interactions
N-Linked glycans are also key to cell-cell interactions. In cancer cells, abnormal N-Linked glycans are recognized by Natural Killer cells as a cancer-like behavior. N-Linked glycans on the surface of immune cells help determine the cell's migration pattern, and specific glycosylation patterns enable immune cells to accurately respond to infection or other immune challenges.
The number and structure of N-Linked glycans can affect the efficacy of antibodies and thus the outcome of the immune response.
Conclusion
With in-depth research on N-Linked glycans, scientists are gradually revealing their importance in cell biology and their complex relationship with diseases. Future research may reveal more about the role of sugars in cell biology and disease mechanisms and suggest new potential treatments. As we rethink the role of sugars in various biological processes, what breakthroughs and innovations do you think glycoscience will bring in the future?
