Selective depolymerisation of dermatan sulfate: Production of radiolabelled substrates for α- l-iduronidase, sulfoiduronate sulfatase, and β- d-glucuronidase

Abstract

Radiolabelled disaccharide substrates for α- l-iduronidase, β- d-glucuronidase, and sulfoiduronate sulfatase have been prepared from dermatan sulfate by application in sequence of N-deacetylation, deaminative cleavage, and reduction with NaBT 4. The yield of disaccharides was ∼87% of the total oligosaccharide fraction. Five disaccharides were isolated and tentatively identified. The major disaccharide, O-(α- l-idopyranosyluronic acid)-(1→3)-2,5-anhydro- d-[1- 3H]talitol 4-sulfate (IdoA-anT4S), represented ∼75% of the total disaccharide fraction. The other disaccharides were O-(α- l-idopyranosyluronic acid 2-sulfate)-(1→3)-2,5-anhydro- d-[1- 3H]talitol 4-sulfate (IdoA2S-anT4S), O-(β- d-glucopyranosyluronic acid)-(1→3)-2,5-anhydro- d-[1- 3H]talitol 4-sulfate (GlcA-anT4S), O-(β- d-glucopyranosyluronic acid)-(1→3)-2,5-anhydro- d-[1- 3H]talitol 6-sulfate (GlcA-anT6S), and O-(α- l-idopyranosyluronic acid)-(1→3)-2,5-anhydro- d-[1- 3H]talitol (IdoA-anT), which represented ∼4.5, 11.2, 1.0, and 1.8%, respectively, of the total disaccharide fraction. When incubated with cultured skin-fibroblasts from normal controls, IdoA-anT4S was shown to be a sensitive substrate for α- l-iduronidase to produce 2,5-anhydro- d-talitol 4-sulfate (anT4S). Activity toward IdoA-anT4S was not observed with fibroblast homogenates from α- l-iduronidase-deficient patients (Mucopolysaccharidosis Type I). Similarly, normal-fibroblast homogenates degraded GlcA-anT6S to anT6S, and GlcA-anT4S to anT4S, at a rate 6 to 8 times greater than found for fibroblasts from β- d-glucuronidase-deficient patients (Mucopolysaccharidosis Type VII). IdoA-anT4S was hydrolysed by α- l-iduronidase at a rate 365 times greater than that for IdoA-anT. Sulfation of the anhydro- d-[1- 3H]talitol residues is an important structural determinant in the mechanism of action of α- l-iduronidase on disaccharide substrates. IdoA2S-anT4S was degraded to IdoA-anT4S and then to anT4S by normal-fibroblast homogenates, whereas fibroblasts from α- l-iduronidase-deficient and sulfoiduronate sulfatase-deficient (Mucopolysaccharidosis Type II) patients produced considerably decreased levels of anT4s and IdoA-anT4S (and anT4S), respectively.