Glycoprotein with sialic acid Addition of alpha-2,8-sialic acid to N-glycan over a galactose by ST8SIAs Addition of sialic acid to galactose-containing N-glycan. Sialic acid is usually found at terminal positions of the N-glycan. This imparts a negative charge at neutral pH this adds a negative charge which affects the chemico-physical and biological properties of the N-glycans (for a review, see Schauer R 2000); moreover, this modification can lead to the addition of extraordinarily long antennae such as polysialic acid (hundreds of sials) or poly lactosamine repeats (dozens of disaccharide repeats) (Harduin-Lepers A, 2001), while the number of modifications on the antennae of N-glycans is usually lower.<br>There are over 20 sialyltransferases known in humans, 5 of which are known to act on N-glycans. ST6Gal I (ST6GAL1) is the only alpha-2,6-sialyltransferase known to transfer sialic acid to galactose on N-Glycans (Dall'Olio F, 2000). A second beta-Galactoside alpha-2,6-sialyltransferase has been characterized, but this enzyme acts mainly on oligosaccharides (Krzewinski-Recchi MA et al 2003). Sialic acids can also be added via an alpha-2,3-linkage to galactose on N-glycans by ST3GalIV(ST3GAL4) (Ellies et al 2002). ST8Sia II (ST8SIA2), ST8Sia III (ST8SIA3), and ST8Sia IV (ST8SIA6) have alpha-2,8-activity (Angata K et al 1997; Angata et al 2000; Angata K, Fuduka M 2003). Authored: Dall'Olio, GM, 2009-11-10 EC Number: 2.4.99.8 Edited: Jassal, B, 2010-10-08 Pubmed10766765 Pubmed11421344 Pubmed11425186 Pubmed11530204 Pubmed12097641 Pubmed12603328 Pubmed12765789 Pubmed9054414 Reactome Database ID Release 431022133 Reactome, http://www.reactome.org ReactomeREACT_25115 Reviewed: Gagneux, P, 2010-11-18