Sulfation of sialyl N-acetyllactosamine oligosaccharides and fetuin oligosaccharides by keratan sulfate Gal-6-sulfotransferase

We have previously cloned keratan sulfate Gal-6-sulfotransferase (KSGal6ST), which transfers sulfate from 3'-phosphoadenosine 5'-phosphosulfate to position 6 of Gal residue of keratan sulfate. In this study, we examined whether KSGal6ST could transfer sulfate to sialyl N-acetyllactosamine oligosaccharides or fetuin oligosaccharides. KSGal6ST expressed in COS-7 cells catalyzed transfer of sulfate to NeuAc alpha 2-3Gal beta 1-4GlcNAc (3'SLN), NeuAc alpha 2-3Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4GlcNAc (SL1L1), NeuAc alpha 2-3Gal beta 1-4(6-sulfo)GlcNAc beta 1-3(6-sulfo)Gal beta 1-4(6-sulfo)GlcNAc (SL2L4), and their desialylated derivatives except for Gal beta 1-4GlcNAc, but not to NeuAc alpha 2-3Gal beta 1-4(Fuc alpha 1-3)GlcNAc (SLex). When the sulfated product formed from 3'SLN was degraded with neuraminidase and reduced with NaBH4, the resulting sulfated disaccharide alditol showed the same retention time in SAX-HPLC as that of [H-3]Gal(6SO(4))beta 1-4GlcNAc-ol. KSGal6ST also catalyzed sulfation of fetuin, When the sulfated oligosaccharides released from the sulfated fetuin after sequential digestion with proteinase and neuraminidase were subjected to a reaction sequence of hydrazinolysis, deaminative cleavage and NaBH4 reduction, the major product was co-eluted with [H-3]Gal(6SO(4))beta 1-4anhydromannitol in SAX-HPLC. These observations show that KSGal6ST is able to sulfate position 6 of Gal residue of 3'SLN and fetuin oligosaccharides, The relative rates of the sulfation of SL2L4 was much higher than the rate of the sulfation of keratan sulfate, These results suggest that KSGal6ST may function in the sulfation of sialyl N-acetyllactosamine oligosaccharide chains attached to glycoproteins.