Nacetylneuraminic

N-acetylneuraminic acid, commonly abbreviated Neu5Ac, is the most abundant sialic acid in humans and many other animals. It is a nine-carbon acidic sugar (neuraminic acid) bearing an N-acetyl group and is typically found at the outermost ends of glycoconjugates on cell surfaces, where it is usually linked to underlying sugars by α2-3, α2-6, or α2-8 glycosidic bonds.

Biological context and distribution: Neu5Ac residues cap glycoproteins and glycolipids, contributing to the negative charge and hydrophilicity of the cell surface. This terminal position influences protein stability, receptor interactions, and cell–cell communication. Sialylation patterns vary across tissues and developmental stages and are recognized by various lectins, including siglecs, which modulate immune signaling.

Biosynthesis and metabolism: In vertebrates, Neu5Ac is synthesized in the cytosol from UDP-N-acetylglucosamine through a multi-step pathway that produces N-acetylmannosamine, which is ultimately converted to Neu5Ac. It is activated to CMP-Neu5Ac by CMP-sialic acid synthetase and transported into the Golgi apparatus, where sialyltransferases attach Neu5Ac to glycoconjugates. Free Neu5Ac can be recycled or degraded by neuraminidases, releasing free sialic acid.

Function and clinical relevance: Sialic acids influence pathogen interactions, as many microbes and viruses target sialylated surfaces; for example, influenza virus binds to sialic acid residues via hemagglutinin. Altered sialylation is associated with certain diseases, including cancer and inflammatory conditions, making Neu5Ac-containing glycans a focus of diagnostic and therapeutic research.