Recombinant human iduronate-2-sulphatase: correction of mucopolysaccharidosis-type II fibroblasts and characterization of the purified enzyme

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Abstract
Mucopolysaccharidosis type II (MPS II, Hunter syndrome) is an X-chromosome-linked recessive lysosomal storage disorder that results from a deficiency of iduronate-2-sulphatase (12S). Patients with MPS II store and excrete large amounts of partially degraded heparan sulphate and dermatan sulphate. In order to evaluate enzyme-replacement therapy for MPS II we have expressed a chimaeric I2S cDNA in CHO (Chinese-hamster ovary)-K1 cells utilizing a plasmid vector that places the cDNA under the transcriptional control of the human polypeptide-chain-elongation factor-1 alpha gene promoter. A clonal cell line that accumulated recombinant I2S at greater than 10 mg/ml in conditioned medium was identified. Enzyme secreted from this cell line grown in the presence of NH4Cl was shown to be endocytosed into MPS II fibroblasts via the mannose 6-phosphate receptor and localized to the lysosomal compartment, resulting in correction of the storage phenotype of these cells. Milligram quantities of the recombinant I2S were purified, and the enzyme was shown to have a pH optimum and kinetic parameters similar to those for the mature form of I2S purified from human liver. The recombinant I2S had a molecular mass of approx. 90 kDa; this was reduced to 60 kDa by endoglycosidase treatment.