Lysosomal Targeting Enhancement by Conjugation of Glycopeptides Containing Mannose-6-phosphate Glycans Derived from Glyco-engineered Yeast

Many therapeutic enzymes for lysosomal storage diseases require a high content of mannose-6-phosphate (M6P) glycan, which is important for cellular uptake and lysosomal targeting. We constructed glyco-engineered yeast harboring a high content of mannosylphosphorylated glycans, which can be converted to M6P glycans by uncapping of the outer mannose residue. In this study, the cell wall of this yeast was employed as a natural M6P glycan source for conjugation to therapeutic enzymes. The extracted cell wall mannoproteins were digested by pronase to generate short glycopeptides, which were further elaborated by uncapping and α(1,2)-mannosidase digestion steps. The resulting glycopeptides containing M6P glycans (M6PgPs) showed proper cellular uptake and lysosome targeting. The purified M6PgPs were successfully conjugated to a recombinant acid α-glucosidase (rGAA), used for the treatment of Pompe disease, by two-step reactions using two hetero-bifunctional crosslinkers. First, rGAA and M6PgPs were modified with crosslinkers containing azide and dibenzocyclooctyne, respectively. In the second reaction using copper-free click chemistry, the azide-functionalized rGAA was conjugated with dibenzocyclooctyne-functionalized M6PgPs without the loss of enzyme activity. The M6PgP-conjugated rGAA had a 16-fold higher content of M6P glycan than rGAA, which resulted in greatly increased cellular uptake and efficient digestion of glycogen accumulated in Pompe disease patient fibroblasts.