Sialic Acid

Description:Sialic acid is a generic term for the N- or O-substituted derivatives of neuraminic acid, a monosaccharide with a nine-carbon backbone.[1] 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 species ranging from plants and fungi to yeasts and bacteria, mostly in glycoproteins and gangliosides. The amino group generally bears either an acetyl or glycolyl group but other modifications have been described.Sialic acid-rich glycoproteins (sialoglycoproteins) bind selectin in humans and other organisms. Metastatic cancer cells often express a high density of sialic acid-rich glycoproteins.[citation needed] 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 hemagglutinin 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.