sialoglycans

Sialoglycans are glycans that contain sialic acid residues, most commonly N-acetylneuraminic acid (Neu5Ac), linked to underlying sugars on glycoproteins and glycolipids. Sialic acids are typically terminal units on N- and O-linked oligosaccharides and can also be found in extended polysialic acid chains on certain glycoproteins such as neural cell adhesion molecule (NCAM). The most common linkages are α2-3 and α2-6 from sialic acid to galactose, with additional α2-8 linkages forming polysialic chains or present in ganglioside backbones.

Biosynthesis and structure arise in the Golgi, where sialyltransferases transfer CMP-Neu5Ac to acceptor sugars. The pattern of sialylation is determined by the repertoire of sialyltransferases and remodeling enzymes; neuraminidases can remove sialic acids. In humans, the predominant sialic acid is Neu5Ac, while endogenous synthesis of Neu5Gc is absent due to CMAH inactivation; Neu5Gc can still be acquired from the diet and incorporated into glycoconjugates.

Functional roles of sialoglycans are diverse. They influence protein solubility and circulatory half-life by masking galactose residues that would target glycoproteins for receptor-mediated clearance. They mediate interactions with lectins such as siglecs and selectins and modulate pathogen binding. Sialoglycan patterns change during development, aging, and disease; hypersialylation is commonly observed in cancer and can contribute to immune evasion and metastatic potential.

Analytical and clinical aspects include study by lectin binding and mass spectrometry, chromatography, and glycan sequencing. Abnormal sialylation is investigated as a biomarker in cancer and inflammatory diseases, and altered sialoglycan patterns are a focus of glycobiology research.