sialylaatio

Sialylaatio, commonly called sialylation, is the biochemical process by which sialic acid residues are enzymatically added to glycoproteins and glycolipids on cell surfaces and in secreted proteins. In animals, this modification occurs mainly in the Golgi apparatus and is carried out by sialyltransferase enzymes that transfer a sialic acid donor, CMP-N-acetylneuraminic acid (CMP-Neu5Ac), to terminal galactose or N-acetyllactosamine structures.

Sialyltransferases form several families, including ST3Gal, ST6Gal, ST6GalNAc, and ST8Sia, each with specific linkage preferences. Common linkages include alpha-2,3 and alpha-2,6 to galactose, as well as alpha-2,8 in polysialylation. The pattern and extent of sialylation influence the stability, half-life, and biological recognition of glycoproteins and glycolipids, affecting cell–cell interactions, receptor binding, and immune responses.

Biological significance is broad. Sialylation can shield underlying sugar motifs from lectins and proteases, regulate protein clearance from the bloodstream by the asialoglycoprotein receptor, and modulate interactions with immune receptors such as Siglecs. It also affects selectin-mediated cell trafficking, neural development, and pathogen interactions, since many microbes and toxins recognize or mimic sialic acid patterns.

Abnormal sialylation is associated with disease and clinical relevance. Altered sialylation patterns occur in cancer, inflammation, and congenital disorders of glycosylation. In biotechnology, the sialylation state of therapeutic proteins influences efficacy and half-life, motivating both efforts to engineer sialylation and strategies to inhibit specific sialyltransferases.

Research methods to study sialylation include lectin binding assays using sialic-acid–specific lectins, mass spectrometry and chromatography for glycan profiling, and metabolic labeling with azido-sugars followed by click chemistry.