Sialic acid

Sialic acid is a generic term for the N- or O-substituted derivatives of neuraminic acid, a monosaccharide with a nine-carbon backbone. It is also the name for the most common member of this group, N-acetylneuraminic acid (Neu5Ac or NANA). Sialic acids are found widely distributed in animal tissues and to a lesser extent in other organisms, ranging from fungi to yeasts and bacteria, mostly in glycoproteins and gangliosides.

Structure and occurrence

Sialic acids are a type of monosaccharides that are derivatives of neuraminic acid. They have a nine-carbon backbone. The most common member of these acids is N-acetylneuraminic acid (Neu5Ac or NANA). They are found in animal tissues and to a lesser extent in other organisms, ranging from fungi to yeasts and bacteria. They are mostly found in glycoproteins and gangliosides.

Function

Sialic acids are important in biology and pathology. They are crucial components of several different types of glycoconjugates, including glycolipids, glycoproteins, and proteoglycans. They are also involved in various biological functions, such as cell-cell interaction, immunity, and pathogenesis.

Biosynthesis

The biosynthesis of sialic acid involves the enzyme UDP-N-acetylglucosamine 2-epimerase, which catalyzes the epimerization of N-acetylglucosamine (GlcNAc) to N-acetylmannosamine (ManNAc), and the subsequent transfer of the acetyl group to a cytidine molecule, forming CMP-N-acetylneuraminic acid.

Role in disease

Sialic acids play a significant role in many diseases, including cancer, influenza, and bacterial infections. In cancer, changes in the sialic acid composition of cells can lead to abnormal cell-cell interactions and metastasis. In influenza, the virus binds to sialic acids on the surface of human cells, allowing it to infect the cell. In bacterial infections, some bacteria use sialic acids as a nutrient source, while others use them to evade the immune system.

See also

• Neuraminidase
• Sialidase
• Sialyltransferase

Sialic acid

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  Neu5Ac
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  Beta Neuraminic acid
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  Sialic acids 1
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  Sialic acids 2
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  Sialic acid and the influenza virus