Enhanced activity of recombinant β-secretase from Drosophila melanogaster S2 cells transformed with cDNAs encoding human β1,4-galactosyltransferase and Galβ1,4-GlcNAc α2,6-sialyltransferase

β-Secretase (βSEC) was expressed in Drososphila melanogaster Schneider 2 (S2) cells transformed with cDNAs encoding β1,4-galactosyltransferase (GalT) and Galβ1,4-GlcNAc α2,6-sialyltransferase (ST). The apparent molecular weight of recombinant β-secretase was increased from 56 kDa to 61 kDa. A lectin blot analysis indicated that recombinant β-secretase from S2βSEC/GalT-ST cells (S2 cells co-transformed with cDNAs encoding β-secretase, glycosyltransferases, GalT, and ST) contained the glycan residues of β1,4-linked galactose and α2,6-linked sialic acid. Two dimensional electrophoresis revealed that recombinant β-secretase from S2βSEC/GalT-ST cells had a lower isoelectric point compared to β-secretase from control S2βSEC cells (S2 cells transformed only with β-secretase cDNA). Recombinant β-secretase from transformed S2 cells was also present as heterogeneous forms. The enzyme activity of recombinant β-secretase from S2βSEC/GalT-ST cells was enhanced up to 260% compared to control S2βSEC cells. We have shown that an exogeneous human glycosyltransferases cDNA can be introduced into S2 cells to extend the N-glycan processing capabilities of the insect cell line, and that the extended glycosylation improves the activity of recombinant β-secretase.