Expression of a mammalian alpha 2,6-sialyltransferase gene in Pichia pastoris

Terminal sialic acid on oligosaccharides of glycoproteins shows several biological functions of the glycoproteins. The yeast Pichia pastoris normally does not contain sialic acid on the oligosaccharides of glycoproteins. A sialyltransferase (ST) gene was transfected into P. pastoris to assess the possibility of using yeast cells as a host to produce sialoglycoproteins. The expression vectors pPIC3.5 and pPIC9 were used as carriers. The recombinant P. pastoris harbouring ST-pPIC3.5 and ST-pPIC9 had sialyltransferase activity of 1.1 and 10.2 mU l(-1) respectively. The ability of the recombinant ST-pPIC3.5 and ST-pPIC9 to transfer the fluoresceinyl-NeuAc into the cell glycoproteins was 36.9 and 20.9 pmol mg -1 protein respectively.