CMP-NeuAc:Galβ1→4GlcNAc α2→6sialyltransferase catalyzes NeuAc transfer to glycolipids

Using mammalian gene-overexpression system, in vitro catalytic activities of CMP-NeuAc:Galβ1→4GlcNAc α2→6sialyltransferase on glycosphingolipid acceptors were analyzed. We transfected the mammalian expression vector containing the cDNA that was cloned from Daudi cells into COS-1 cells, and selected monoclonal transfectants in the presence of G418. Although the transfectedα2→6sialyltransferase can catalyze NeuAc transfer onto glycoprotein acceptors more than glycolipids based on kinetic analyses, the substantial synthesis of IV⁶NeuAc-nLcOse₄Cer was observed and the activities were 7-to 9-times higher in the transfected cells than in the mock transfectants. In addition, the transfected COS-1 cells with α2→6sialyltransferase cDNA were revealed to contain a higher amount of ganglioside that has the terminal NeuAcα2→6Gal sequence in the in situ situation than the mock transfectants. These results using transfectants, together with those using the purified enzyme protein, suggest that the α2→6sialyltransferase enzyme from Daudi cells can also catalyze NeuAc transfer in α2→6 linkage onto glycosphingolipid acceptors.