Expression of catalytically active human multifunctional glycogen-debranching enzyme and lysosomal acid alpha-glucosidase in insect cells.

Glycogen debranching enzyme and acid alpha-glucosdase are responsible for glycogen degradation in human. The formal enzyme is a multifunctional enzyme with two independent catalytic activities occurring on a single polypeptide, while the latter is a lysosomal enzyme which matures through extensive glycosylation and phosphorylation and proteolytic processing. Deficiency of glycogen debranching enzyme and acid alpha-glucosidase cause glycogen storage disease type III and II, respectively. Baculovirus/insect expression system was used to produce both GDE and GAA. Both enzymes were found to be catalytically and antigenically active. The majority of recombinant GDE is present in the medium (70%). Uptake experiment indicated that GAA produced in the insect cells could not be absorbed into the GSD type II patient fibroblasts through mannose-6-phosphate receptor mediated endocytosis. Uptake experiment combined with immunoblot analysis indicated there are differences in the posttranslational modification and processing between insect cells and mammalian cells.