What is the Difference Between N Glycosylation and O Glycosylation?

N-glycosylation and O-glycosylation are two types of protein glycosylation that differ in several aspects:

1. Glycan linkages: In N-linked glycosylation, a protein can exhibit multiple glycan linkages, ranging from one to many. In contrast, O-linked glycosylation typically includes only a single sugar residue added to a serine or threonine residue.
2. Amino acid involvement: N-linked glycosylation involves the glycan being connected to the nitrogen atom of the amino acid asparagine (N), while O-linked glycosylation involves the glycan being connected to the oxygen atom of the amino acids serine or threonine (O).
3. Glycan structure: N-linked glycosylation results in a more complex and branched glycan structure compared to O-linked glycosylation, which is typically less branched and often biantennary.
4. Occurrence: N-linked glycosylation is the most abundant form of glycosylation in eukaryotic cells, accounting for over 90% of all glycosylation events. O-linked glycosylation, on the other hand, is more common in bacteria and has a simpler biosynthetic pathway.
5. Subcellular location: N-linked glycosylation begins in the endoplasmic reticulum, while O-linked glycosylation occurs in the Golgi apparatus.

Both N-linked and O-linked glycosylation are highly regulated processes, and they can cross-regulate each other. For example, O-linked glycosylation can affect the efficiency and specificity of N-linked glycosylation, and the enzyme responsible for N-linked glycosylation can be regulated by O-linked glycosylation.

Comparative Table: N Glycosylation vs O Glycosylation

Here is a table comparing the differences between N-glycosylation and O-glycosylation:

N-linked glycosylation involves the attachment of an oligosaccharide sugar molecule to the nitrogen atom of the amino acid asparagine, while O-linked glycosylation involves the attachment of a sugar molecule to the oxygen atom of the amino acid serine or threonine. The core structure of N-linked glycosylation is composed of two N-acetylglucosamine (GlcNAc) and nine mannose (Man) molecules, while the core structure of O-linked glycosylation is composed of a single GalNAc molecule. N-linked glycosylation typically involves multiple glycan linkages, ranging from one to many, whereas O-linked glycosylation typically includes only a single sugar residue added to a serine or threonine.