How would glycosylating a protein affect its pI? I reasoned that it would increa

Question

How would glycosylating a protein affect its pI? I reasoned that it would increase pI, because first, I thought that pI is the average between all the pKa's. I thought that the pKa of a few glycosylations would be higher, since we would want a lower Ka to make sure that the H+'s of the OH groups are all attached to make a neutral atom. Therefore, the pKa's of the glycosylations would be higher. This would mean that the pI would be higher.

What I was confused about is that if the solution needs to be more alkaline for the protein to be neutral, that would mean that there are more OH-'s in the solution. I'd think that this would rip away the H+'s from the glycosylations making it negatively charged... With this reasoning, shouldn't the pI be lower so that there is more Hydrogens in the solution so that the attached sugars would stay neutral?

Explanation / Answer

Glycosylation of protein effect the surface Lysine charge as a result in decrease of isoelectric point of protein and increase the stability of protein. Another reason of change in pI of a protein after glycoslation is terminal end glycans are often added with cahrged functional group like sulfate, phosphate or carboxylic acids etc. that changes the overall charge of the protein surface and leads to change in pI of the protein.

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