Neuraminic

Neuraminic is an adjective used in biochemistry to refer to neuraminic acid and, more broadly, to the family of sialic acids that share a nine-carbon backbone and an acidic carboxyl group. Sialic acids are typically found at the outermost ends of glycoprotein and glycolipid chains on animal cell surfaces and in some microbial glycoconjugates.

The most common natural sialic acids are N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc). These molecules occur as various derivatives formed by acetylation, glycolylation, and other modifications, and they are negatively charged at physiological pH. They are often present as terminal residues on glycans, influencing recognition, hydration, and the stability of glycoconjugates.

Biosynthesis and distribution: sialic acids are synthesized in cells and activated as CMP-sialic acid, which is transferred to glycans in the Golgi apparatus. In vertebrates, sialic acids decorate many glycoproteins and glycolipids, contributing to the negative surface charge and diverse biological interactions.

Functional roles: sialic acids mediate cell–cell and pathogen–host interactions, modulate immune recognition, and affect the circulatory half-life of glycoproteins. They can mask underlying glycans to influence immune detection. Pathogens often exploit sialic acids for attachment, while microbial and viral enzymes (neuraminidases) cleave them to promote entry, spread, or release.

Human relevance: the major endogenous sialic acid is Neu5Ac. Humans do not synthesize Neu5Gc due to loss of the CMAH gene, though dietary Neu5Gc can be incorporated into tissues and may provoke immune responses in certain contexts.