Sialic acid

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Sialic acid

Identifiers
CAS number	[131-48-6]
PubChem	445063
MeSH	Sialic+Acid
Properties
Molecular formula	C₁₁H₁₉NO₉
Molar mass	309.273
Appearance	White crystalline powder
Melting point	186°C (decomposes)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references

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 in bacteria, especially in glycoproteins and gangliosides. The amino group bears either an acetyl or a glycolyl group. The hydroxyl substituents may vary considerably: acetyl, lactyl, methyl, sulfate, and phosphate groups have been found.^[1]

Sialic acid-rich glycoproteins bind selectin in humans and other organisms. Cancer cells that can metastasize often have a lot of sialic acid-rich glycoproteins. This helps these late-stage cancer cells enter the blood stream.

Sialic acid also plays an important role in Human Influenza infections. The influenza viruses (orthomyxoviridae) have Hemagglutin Activity (HA) glycoproteins on their surface that bind to sialic acids found on the surface of human erythrocytes and on the cell membranes of the upper respiratory tract. This is the basis of heme-agglutination when viruses are mixed with blood cells, and entry of the virus into cells of the upper respiratory tract.

Sialic acid-rich oligosaccharides on the glycoconjugates found on surface membranes help keep water at the surface of cells. The sialic acid-rich regions contribute to creating a negative charge on the cells' surface. Since water is a polar molecule with partial positive charges on both hydrogen atoms, it is attracted to cell surfaces and membranes. This also contributes to cellular fluid uptake.

Sialic acid can "hide" mannose antigens on the surface of host cells or bacteria from mannose-binding lectin. This prevents activation of complement.

The term "sialic acid" (from the Greek σιαλοσ (sialos) 'saliva') was first introduced by Swedish biochemist, Gunnar Blix, in 1952.