Arylsulfatase A from human placenta possesses only high mannose-type glycans

It has been shown that the concentration of arylsulfatase A increases in the body fluids of patients with some forms of cancer and the carbohydrate component of arylsulfatase A synthesized in tumor tissues and transformed cells undergoes increased sialylation, phosphorylation and sulfation. The specificity of changes in the glycosylation of glycoproteins in cancer is still unknown. To understand the significance of any changes in glycosylation of arylsulfatase A in cancer, it is important to know the structure of its carbohydrate component in normal tissue. Here, carbohydrate moieties of human placental arylsulfatase A were studied by sequential lectin affinity chromatography after enzymatic cleavage and labelling with tritiated sodium borohydride. Labelled oligosaccharides were subjected to ion exchange chromatography. The uncharged fraction and the neuraminidase treated charged fraction were further analysed using the lectins: Concanavalin A (Con A), Ricinus communis (RCA I), Triticum vulgaris (L-PHA) and Aleuria aurantia (AAL). The results indicated that 97% of the arylsulfatase A oligosaccharides were low molecular weight high mannose type glycans possessing up to 5 mannose residues. This was supported by the approximately 2.4 kDa decrease in the molecular weight of arylsulfatase. A subunits upon complete peptide N-glycosidase F deglycosylation, as shown using SDS-PAGE. The remaining 3% of the arylsulfatase A oligosaccharides were of the high mannose type, possessing more than 5 mannose residues. Most (97.5%) of the glycans were uncharged, while 2.5% were charged. Neuraminidase treatment of the latter did not remove the charge, suggesting the presence of phosphate or sulfate residues. This study, of arylsulfatase A oligosaccharides separated from the protein part, shows that all glycans of the enzyme from human placenta are of the high mannose type.