Enhancement of sialyltransferase-catalyzed transfer of sialic acid onto glycoprotein oligosaccharides using silkworm hemolymph and its 30K protein

Silkworm hemolymph (SH) has been reported to inhibit apoptosis in both insect and human cells, and increase the high-sialylation structure of recombinant glycoprotein in insect cells. This indicates that SH might increase glycosyltransferase activity. Therefore, this study examined the effect of SH on the activity of sialyltransferase, which catalyzes the sialylation of the glycoprotein. When 10 μg/mL of SH was added to the reaction mixture, almost complete sialylation was observed even under the reaction conditions where sialyltransferase-catalyzed sialylation rarely occurs. The effect of deproteinized SH (dSH) and the 30K protein, which is a major plasma protein in SH, was examined to determine which component in SH enhances sialylation. The 30K protein promoted sialylation, while the dSH did not. This suggests that SH and its 30K protein can be used as an additive to a medium for efficient glycosylation when mammalian cells are being cultured for the production of valuable biopharmaceuticals, many of which are glycoproteins.