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In enzymology, a N-acetyllactosaminide alpha-2,3-sialyltransferase (EC 2.4.99.6) is an enzyme that catalyzes the chemical reaction

CMP-N-acetylneuraminate + beta-D-galactosyl-1,4-N-acetyl-D-glucosaminyl-glycoprotein ${\displaystyle \rightleftharpoons }$ CMP + alpha-N-acetylneuraminyl-2,3-beta-D-galactosyl-1,4-N-acetyl-D- glucosaminyl-glycoprotein

Thus, the two substrates of this enzyme are CMP-N-acetylneuraminate and beta-D-galactosyl-1,4-N-acetyl-D-glucosaminyl-glycoprotein, whereas its 3 products are CMP, alpha-N-acetylneuraminyl-2,3-beta-D-galactosyl-1,4-N-acetyl-D-, and glucosaminyl-glycoprotein.

This enzyme belongs to the family of transferases, specifically those glycosyltransferases that do not transfer hexosyl or pentosyl groups. The systematic name of this enzyme class is CMP-N-acetylneuraminate:beta-D-galactosyl-1,4-N-acetyl-D-glucosaminy l-glycoprotein alpha-2,3-N-acetylneuraminyltransferase. Other names in common use include sialyltransferase, cytidine, monophosphoacetylneuraminate-beta-galactosyl(1-, >4)acetylglucosaminide alpha2->3-sialyltransferase, alpha2->3 sialyltransferase, and SiaT. This enzyme participates in 4 metabolic pathways: keratan sulfate biosynthesis, glycosphingolipid biosynthesis - lactoseries, glycan structures - biosynthesis 1, and glycan structures - biosynthesis 2.

Structural studies

As of late 2007, two structures have been solved for this class of enzymes, with PDB accession codes 2EX0 and 2EX1.

References

• Van den Eijnden DH, Schiphorst WE (1981). "Detection of beta-galactosyl(1 leads to 4)N-acetylglucosaminide alpha(2 leads to 3)-sialyltransferase activity in fetal calf liver and other tissues". J. Biol. Chem. 256 (7): 3159–62. doi:10.1016/S0021-9258(19)69581-5. PMID 7204397.

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