Difference Between Glycation and Glycosylation

The key difference between glycation and glycosylation is that glycation is not an enzymatic process while glycosylation is an enzymatic process.

Both glycation and glycosylation are two processes that add sugar molecules to proteins. Glycation is a non-enzymatic process of adding free sugars to protein covalently, which occurs spontaneously in the bloodstream. Glycosylation, on the other hand, is a post-translational modification process that takes place in the endoplasmic reticulum and Golgi apparatus while producing a functional protein. Even though there are some similarities between glycation and glycosylation, this article discusses the difference between glycation and glycosylation.

CONTENTS

1. Overview and Key Difference
2. What is Glycation
3. What is Glycosylation
4. Similarities Between Glycation and Glycosylation
5. Side by Side Comparison – Glycation vs Glycosylation in Tabular Form
6. Summary

What is Glycation?

Glycation is a non-enzymatic process that covalently adds free sugars to protein. Since it is non-enzymatic, glycation occurs spontaneously in the bloodstream. Hence, this process is not under the control of an enzyme. Glycation irreversibly adds sugars or sugar degradative products to proteins. Moreover, glycation is a type of protein-damaging process. Therefore, it reduces the stability and functionality of proteins.

Glucose, fructose or galactose are the sugars added during glycation. By glycation, the addition of sugars only takes place in mature proteins. The first step of glycation is condensation. It is a time-consuming process. The end product of condensation is a non-stable Shiff base or aldimine. Then, aldimine spontaneously rearranges to form the Amadori product, which is a stable keto amine. Then, this product undergoes further degradation. Advanced glycation end products is the name we use for final products of glycation.

What is Glycosylation?

Glycosylation is a post-translational modification process that takes place in the endoplasmic reticulum and Golgi apparatus. Moreover, glycosylation facilitates proper protein folding and thereby uplifts the stability of the protein. Hence, this process produces a functional protein as the end product.

Moreover, this is an enzyme regulated process. Hence, we can define it as an enzymatic modification. Here, a defined sugar molecule is added to a predefined region of a protein. The regulation of this process occurs via the regulation of the action of the enzyme.

There can be several types of glycosylation. They are N-linked glycosylation O-linked glycosylation, phosphoserine glycosylation, etc. Generally, during glycosylation, the carbonyl part of the sugar reacts with the amine or hydroxyl group of the protein.

What are the Similarities Between Glycation and Glycosylation?

• Both glycation and glycosylation add sugars to proteins.
• During both processes, covalent bonds are built up between the molecules.
• Both are cellular processes.
• Moreover, both processes affect the functionality of a protein.

What is the Difference Between Glycation and Glycosylation?

Glycation is a non-enzymatic process that covalently adds free sugars to protein while glycosylation is an enzymatic post-translational modification process occurring in the endoplasmic reticulum and Golgi apparatus, which produces a functional protein. Therefore, we can consider this as the key difference between glycation and glycosylation. Furthermore, glycation is a spontaneous process; hence, it is not regulated by an enzyme. But, glycosylation is a fully enzyme-regulated process. Thus, this is also a difference between glycation and glycosylation.

Moreover, glycation reduces the stability and functionality of proteins. However, glycosylation produces a functional protein through the addition of sugar molecules. In addition, a further difference between glycation and glycosylation is that the glycation adds glucose, fructose or galactose to proteins while glycosylation adds xylose, fucose, mannose or glycans to proteins. Most importantly, glycosylation increases protein stability while glycation reduces protein stability. So, this is another significant difference between glycation and glycosylation.

The below infographic presents more information regarding the difference between glycation and glycosylation.

Summary – Glycation vs Glycosylation

Both glycation and glycosylation are two processes that add sugar to proteins. Glycation is a non-enzymatic spontaneous process that takes place in the bloodstream. In contrast, glycosylation is an enzyme-mediated process that takes place in the Golgi apparatus and endoplasmic reticulum under post-translational modifications. Furthermore, glycation reduces the stability and functionality of a protein due to the addition of sugars whilst glycosylation converts an immature protein into a functional protein due to the addition of sugars. So, this is a summary of the difference between glycation and glycosylation.

Reference:

1. “Glycosylation.” Thermo Fisher Scientific – US, Available here.
2. Takahashi, Motoko. “Glycation of Proteins.” SpringerLink, Springer, Tokyo, 1 Jan. 1970, Available here.

Image Courtesy:

1. “AGE accumulation” By Jasper Dijkstra – Diagnoptics (CC BY-SA 3.0) via Commons Wikimedia
2. “Glycosylation” By Berninsone, P.M. – Workbook.org (CC BY 2.5) via Commons Wikimedia