N versus O linked glycosylation

[FenderHM]

whats the difference? N in RER O in golgi or something like that? I don;t even really udnerstand what the hell is being glycosylated, I guess transmembrane proteins? ahh!!!!

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[DrJekyl]

N-linked: an entire oligsaccharide is attached to an aspargine residue in the lumen of the ER, then is modified in the golgi.

O-linked: occurs in the golgi, and sugars are added one at a time to a serine or threonine.

I believe glycosylation (O or N) has a wide range of applications in marking cells for recognition.

 

[FenderHM]

cool thanks!

 

[EBI831]

O linked is also in hydroxylysine. called O because it attaches to OH. N-linked names that because its attached to N in amine in asparagine(don't know if its an N b/c of amine or asparagine.

 

[em195]

Yea, finally someone talking about glycosylation! Before I started med school I did my Ph.D. in this field, and it is truly fascinating. A lot of undiscovered roles for sugars are shedding new light on a number of fields, especially immunology and cancer. They permit a protein to alter its function dramatically, without necessarily changing anything at the level of transcription or translation. Very cool stuff.

So, to answer your question: the differences start at the level of the amino acid sequence the sugars are added to. For N-linked, you need an Asn-X-Ser/Thr, and a pre-assembled oligosaccharide is added on to the protein in the rough ER. The precursor is built up, trimmed, and there are chaperone proteins to assure quality control before it's sent off to the cis, medial and trans Golgi for more complex processing. I guess the other important thing is that all N-glycans are put onto proteins that will either be secreted by the cell, or that will be inserted into the plasma membrane - no intracellular proteins get N-glycosylated.

O-linked is a little more complicated. O-linked GlcNAcs can be added to intracellular proteins at sites that would normally be phosphorylated, and this is probably an important mechanism for regulating signal transduction in the cell. O-linked GalNAc residues get added to Serine or Threonine residues (the sequence is not so highly conserved as in N-linked), in the Golgi, and these are more like the N-linked in the sense that they get added to secreted or transmembrane proteins (mostly secreted for O-linked; things like mucins tend to carry a lot of these sugars.)

🙂

 

[slim06]

also very important in I cell disease - crazy - one little glcnac transferase causes all those problems

 

[PsiKo]

Yea, finally someone talking about glycosylation! Before I started med school I did my Ph.D. in this field, and it is truly fascinating. A lot of undiscovered roles for sugars are shedding new light on a number of fields, especially immunology and cancer. They permit a protein to alter its function dramatically, without necessarily changing anything at the level of transcription or translation. Very cool stuff.

So, to answer your question: the differences start at the level of the amino acid sequence the sugars are added to. For N-linked, you need an Asn-X-Ser/Thr, and a pre-assembled oligosaccharide is added on to the protein in the rough ER. The precursor is built up, trimmed, and there are chaperone proteins to assure quality control before it's sent off to the cis, medial and trans Golgi for more complex processing. I guess the other important thing is that all N-glycans are put onto proteins that will either be secreted by the cell, or that will be inserted into the plasma membrane - no intracellular proteins get N-glycosylated.

O-linked is a little more complicated. O-linked GlcNAcs can be added to intracellular proteins at sites that would normally be phosphorylated, and this is probably an important mechanism for regulating signal transduction in the cell. O-linked GalNAc residues get added to Serine or Threonine residues (the sequence is not so highly conserved as in N-linked), in the Golgi, and these are more like the N-linked in the sense that they get added to secreted or transmembrane proteins (mostly secreted for O-linked; things like mucins tend to carry a lot of these sugars.)

🙂

Mm, hmmm... Yeah... Keep talking! 😍