Selective depolymerisation of dermatan sulfate: production of radiolabelled substrates for alpha-L-iduronidase, sulfoiduronate sulfatase, and beta-D-glucuronidase

Radiolabelled disaccharide substrates for alpha-L-iduronidase, beta-D-glucuronidase, and sulfoiduronate sulfatase have been prepared from dermatan sulfate by application in sequence of N-deacetylation, deaminative cleavage, and reduction with NaBT4. The yield of disaccharides was approximately 87% of the total oligosaccharide fraction. Five disaccharides were isolated and tentatively identified. The major disaccharide, O-(alpha-L-idopyranosyluronic acid)-(1 leads to 3)-2,5-anhydro-D-1-3H]talitol 4-sulfate (IdoA-anT4S), represented approximately 75% of the total disaccharide fraction. The other disaccharides were O-(alpha-L-idopyranosyluronic acid 2-sulfate)-(1 leads to 3)-2,5-anhydro-D-1-3H]talitol 4-sulfate (IdoA2S-anT4S), O-(beta-D-glucopyranosyluronic acid)-(1 leads to 3)-2,5-anhydro-D-1-3H]talitol 4-sulfate (GlcA-anT4S), O-(beta-D-glucopyranosyluronic acid)-(1 leads to 3)-2,5-anhydro-D-1-3H]talitol 6-sulfate (GlcA-anT6S), and O-(alpha-L-idopyranosyluronic acid)-(1 leads to 3)-2,5-anhydro-D-1-3H]talitol (IdoA-anT), which represented approximately 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 alpha-L-iduronidase to produce 2,5-anhydro-D-talitol 4-sulfate (anT4S). Activity toward IdoA-anT4S was not observed with fibroblast homogenates from alpha-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 beta-D-glucuronidase-deficient patients (Mucopolysaccharidosis Type VII). IdoA-anT4S was hydrolysed by alpha-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 alpha-L-iduronidase on disaccharide substrates. IdoA2S-anT4S was degraded to IdoA-anT4S and then to anT4S by normal-fibroblast homogenates, whereas fibroblasts from alpha-L-iduronidase-deficient and sulfoiduronate sulfatase-deficient (Mucopolysaccharidosis Type II) patients produced considerably decreased levels of anT4s and IdoA-anT4S (and anT4S), respectively.