The key difference between N-linked and O-linked oligosaccharides is that N-linked oligosaccharides form when N atoms of proteins bind with a sugar, whereas O-linked oligosaccharides form when O atoms of serine or threonine bind with a sugar.
Oligosaccharides are carbohydrate molecules that contain three to six units of monosaccharides or simple sugars. N-linked oligosaccharides are carbohydrate molecules where an oligosaccharide is attached to a nitrogen atom. O-linked oligosaccharides, on the other hand, are a type of carbohydrates where a sugar molecule is attached to an oxygen atom of a serine or threonine residue in a protein.
CONTENTS
1. Overview and Key Difference
2. What are N-linked Oligosaccharides
3. What are O-linked Oligosaccharides
4. N-linked vs O-linked Oligosaccharides in Tabular Form
5. Summary – N-linked vs O-linked Oligosaccharides
What are N-linked Oligosaccharides?
N-linked oligosaccharides are carbohydrate molecules whose oligosaccharides are attached to nitrogen atoms. This occurs through the process of N-glycosylation. Oligosaccharides are carbohydrate compounds containing several sugar molecules. These are sometimes called “glycans.” In the process of N-linked glycosylation, the nitrogen atom usually comes from the amide nitrogen of an asparagine residue of a protein. This process is best described in the field of biochemistry.
Usually, N-linked glycosylation takes place in many eukaryotic proteins. Among eukaryotes, this occurs widely in archaea but rarely in bacteria. We can determine the nature of the N-linked oligosaccharide that is attached to a glycoprotein through the protein and the cell in which it is expressed. The type of N-linked oligosaccharide also depends on the species of organisms.
In a glycoprotein, there are usually two bond types: the bond between saccharide residues in the glycan and the bond between the glycan chain and the protein molecule. There, sugar portions are bonded to each other through glycosidic bonds. The glycosidic bonds are typically C1-C4 bonds. Besides, the bond between an oligosaccharide and a protein residue requires the recognition of a consensus sequence.
What are O-linked Oligosaccharides?
O-linked oligosaccharides are a type of carbohydrates where a sugar molecule is attached to an oxygen atom of a serine or threonine residue in a protein. The process of this bond formation is known as O-linked glycosylation. It is a post-transitional modification process that takes place after the synthesis of a protein.
When considering eukaryotes, this synthesis occurs in the endoplasmic reticulum, Golgi apparatus, and sometimes in the cytoplasm. In prokaryotes, this takes place in the cytoplasm. There are several different types of sugars that can bind with serine or threonine. This binding can affect the protein in different ways. E.g. trafficking of cells in the immune system, which allows the recognition of foreign material.
What is the Difference Between N-linked and O-linked Oligosaccharides?
N-linked oligosaccharides are carbohydrate molecules where the oligosaccharide is attached to a nitrogen atom, while O-linked oligosaccharides are a type of carbohydrates where a sugar molecule is attached to an oxygen atom of a serine or threonine residue in a protein. Therefore, the key difference between N-linked and O-linked oligosaccharides is that N-linked oligosaccharides form when the N atom of proteins bind with a sugar whereas O-linked oligosaccharides form when O atoms of serine or threonine bind with a sugar.
The below infographic presents the differences between N-linked and O-linked oligosaccharides in tabular form for side by side comparison.
Summary – N-linked vs O-linked Oligosaccharides
Oligosaccharides are a type of sugar molecule. The key difference between N-linked and O-linked oligosaccharides is that N-linked oligosaccharides form when N atoms of proteins bind with a sugar, whereas O-linked oligosaccharides form when O atoms of serine or threonine bind with a sugar.
Reference:
1. “Asparagine Linked Oligosaccharide.” An Overview | ScienceDirect Topics.
Image Courtesy:
1. “Variety of glycans” By Dna 621 – Own work (CC BY-SA 3.0) via Commons Wikimedia