Glycosylation of L-asparaginase from E. coli through yeast expression and site-directed mutagenesis

L-Asparaginase (L-ASNase) is a key component in the treatment of acute lymphoblastic leukemia (ALL), but several clinical disadvantages, such as immunogenicity and rapid clearance, are still present. We evaluated the possibility to synthesize a new L-ASNase from Escherichia coll. with human-like glycosylation and study the glycosylation effect on the biochemical properties of the enzyme. Six L-ASNase mutants were also created in which L-ASNase glycosylation sites were removed through site-directed mutagenesis. The WT L-ASNase was successfully expressed, secreted and glycosylated by an engineered P. pastoris strain and presented predominantly Man 5 G1cNAc 2 glycans on its structure, which were then able to decrease L-ASNase immunogenicity in vitro. The purified glycosylated L-ASNase has shown a 30-fold decrease in specific enzymatic activity compared to the non-glycosylated proteoform, but a triple mutant L-ASNase (3M) was able to restore L-ASNase biological activity to significant levels. 3M accumulated in the yeast periplasmic space and there presented a 28fold increase in enzymatic activity when compared to the fully glycosylated proteoform. Both WT and 3M L-ASNases presented increased stability in human serum compared to non-glycosylated L-ASNase. This study demonstrates the important effects of glycosylation on L-ASNase properties and opens up new possibilities to use glycosylated L-ASNases for the treatment of ALL.