protein sialylation

Definition

Target type: biologicalprocess

A protein modification process that results in the addition of a sialic acid unit to the end of an oligosaccharide chain in a glycoprotein. [PMID:21930713]

Sialylation is a crucial post-translational modification in which sialic acids, negatively charged monosaccharides, are attached to the terminal ends of oligosaccharide chains on glycoproteins and glycolipids. This process occurs in the Golgi apparatus, a cellular organelle responsible for protein sorting and modification.

The enzyme responsible for sialylation is sialyltransferase, a glycosyltransferase that catalyzes the transfer of sialic acid from a donor substrate, typically CMP-sialic acid, to an acceptor substrate, the oligosaccharide chain. There are multiple sialyltransferase isoforms, each with distinct substrate specificities and tissue distributions, contributing to the diversity of sialylation patterns observed in various glycoconjugates.

The process of sialylation involves several steps:

1. **Synthesis of CMP-sialic acid:** Sialic acid is synthesized from N-acetylmannosamine and pyruvate, and then activated by the enzyme CMP-sialic acid synthetase, generating CMP-sialic acid, the donor substrate for sialyltransferases.

2. **Transport of CMP-sialic acid to the Golgi:** CMP-sialic acid is transported from the cytoplasm to the Golgi lumen, where sialyltransferases reside.

3. **Recognition and binding of the acceptor substrate:** Sialyltransferases recognize and bind to specific oligosaccharide structures on the acceptor substrate, typically a terminal galactose or N-acetylglucosamine residue.

4. **Transfer of sialic acid:** The sialyltransferase catalyzes the transfer of sialic acid from CMP-sialic acid to the acceptor substrate, forming a glycosidic linkage between the sialic acid and the oligosaccharide chain.

5. **Regulation of sialylation:** Sialylation is tightly regulated, with the activity of sialyltransferases influenced by factors such as cell type, developmental stage, and environmental stimuli.

Sialylation plays a significant role in various biological processes, including:

* **Cell adhesion and recognition:** Sialic acids contribute to the recognition and binding of cells to each other and to extracellular matrix components.
* **Immune regulation:** Sialylation influences the interaction of cells with the immune system, affecting the recognition of pathogens and the activation of immune cells.
* **Signal transduction:** Sialylation can alter the function of glycoproteins involved in signal transduction pathways.
* **Stability and protection:** Sialylation contributes to the stability and protection of glycoproteins against degradation.

Defects in sialylation can lead to various human diseases, including neurological disorders, immunodeficiency, and metabolic diseases. Understanding the intricate process of sialylation is crucial for unraveling the complexity of glycobiology and its role in human health and disease.'
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Proteins (1)

Compounds (11)