Sialylated

Sialylated describes molecules that carry sialic acid residues, typically the nine-carbon acidic sugars such as N-acetylneuraminic acid (Neu5Ac) or its derivatives, appended to glycoproteins and glycolipids. In glycobiology, sialylation refers to the addition of sialic acids to the termini of N-linked or O-linked glycans, as well as to glycosphingolipids (including gangliosides) on cell surfaces and secreted mucins.

Biosynthesis and turnover: Sialyltransferases in the Golgi apparatus catalyze the transfer of sialic acids from CMP-sialic acid donors to underlying sugars; neuraminidases (sialidases) cleave them. Linkages commonly observed include α2-3, α2-6, and α2-8, contributing to diverse recognition by lectins and receptors.

Functional consequences: the negative charge and hydrophilicity of sialic acids influence stability, solubility, and half-life in circulation by reducing recognition by hepatic asialoglycoprotein receptors; removal exposes galactose, leading to clearance. Sialylation modulates interactions with lectins and receptors such as siglecs and selectins, affecting cell adhesion, immune signaling, and pathogen binding.

Clinical relevance: altered sialylation patterns are observed in cancer, inflammation, and genetic glycosylation disorders; changes can influence tumor progression and immune evasion. In humans, the predominant sialic acid is N-acetylneuraminic acid (Neu5Ac); the synthesis of the non-human Neu5Gc is inactive due to CMAH gene loss, making Neu5Gc-containing molecules potentially immunogenic.