Analysis of the specificity of sialyltransferases toward mucin core 2, globo, and related structures. identification of the sialylation sequence and the effects of sulfate, fucose, methyl, and fluoro substituents of the carbohydrate chain in the biosynthesis of selectin and siglec ligands, and novel sialylation by cloned α2,3(O)sialyltransferase

Sialic acids are key determinants in many carbohydrates involved in biological recognition. We studied the acceptor specificities of three cloned sialyltransferases (STs) [α2,3(N)ST, α2,3(O)ST, and α2,6(N)ST] and another α2,3(O)ST present in prostate cancer cell LNCaP toward mucin core 2 tetrasaccharide [Galβ1,4GlcNAcβ1,6(Galβ1,3)GalNAcα-O-Bn] and Globo [Galβ1,3GalNAcβ1,3Galα-O-Me] structures containing sialyl, fucosyl, sulfo, methyl, or fluoro substituents by identifying the products by electrospray ionization tandem mass spectral analysis and other biochemical methods. The Globo precursor was an efficient acceptor for both α2,3(N)ST and α2,3(O)ST, whereas only α2,3(O)ST used its deoxy analogue (d-Fucβ1,3GalNAcβ1,3-Gal-α-O-Me); 2-O-MeGalβ1,3GlcNAc and 4-OMeGalβ1,4GlcNAc were specific acceptors for α2,3(N)ST. Other major findings of this study include:  (i) α2,3 sialylation of β1,3Gal in mucin core 2 can proceed even after α1,3 fucosylation of β1,6-linked LacNAc. (ii) Sialylation of β1,3Gal must precede t...