26sialyltransferase

26 sialyltransferase, commonly referred to as alpha-2,6 sialyltransferase, is a name used for a subset of enzymes that catalyze the transfer of sialic acid to galactose residues in an alpha-2,6 linkage. In humans the principal enzymes are ST6GAL1 and ST6GAL2, which encode Golgi-resident glycosyltransferases responsible for adding sialic acid to glycoproteins and glycolipids. These enzymes are part of the GT29 family of glycosyltransferases and are characterized as type II transmembrane proteins.

Mechanism and localization: The enzymes reside in the Golgi apparatus, where they use the donor substrate CMP-Neu5Ac to transfer sialic acid to acceptor glycans containing galactose residues, generating Neu5Acα2-6Gal linkages.

Substrate scope and products: Substrates include various glycoproteins and glycolipids bearing galactose-containing N- or O-linked glycans. The resulting sialoglycans influence properties of glycoproteins such as stability, circulatory half-life, and recognition by lectins and receptors.

Biological significance: α2-6 sialylation modulates cell–cell interactions, immune responses, and receptor signaling. Altered expression or activity of ST6GAL1/2 affects glycan structures and has been observed in certain diseases, including cancer, inflammatory disorders, and infectious diseases by impacting pathogen binding and immune modulation.

Clinical and research notes: Because sialylation patterns influence inflammation and metastasis, ST6GAL1 and ST6GAL2 are studied as potential biomarkers and therapeutic targets. Species- and tissue-specific expression patterns and regulatory mechanisms continue to be investigated to understand their roles in development and disease.