Presence of glycoproteins containing the polylactosamine structure in brain and liver of GM1 gangliosidosis patients. Comparative study between clinical types I and II, using endo-beta-galactosidase enzyme.

Abstract

The material derived from defective degradation of glycoproteins, which accumulates in brain and liver of a patient with GM1 gangliosidosis type I, was investigated, and the structure of the main storage compounds determined. For comparison, brain and liver of a patient with GM1 gangliosidosis type II were also analyzed. Analysis of the glycopeptides obtained after pronase digestion of the defatted residue indicates the storage of glycoprotein-like material in type I, but not in type II. Treatment with endo-beta-galactosidase showed that the stored material contained N-acetyllactosamine repeating units. Two major oligosaccharides, OS I and OS II, were isolated after the enzyme treatment, whose structures are: GlcNAc beta 1----3 Gal (OS I) and Gal beta l----4GlcNAc beta 1----3 Gal (OS II). Treatment with exo-beta-galactosidase transformed the trisaccharide OS II into the disaccharide OS I, indicating that the deficiency of beta-galactosidase in GM1 gangliosidosis type I, but not in type II, also affects glycoprotein catabolism, leading to the accumulation of glycopeptides containing terminal beta-galactosyl residues and N-acetyllactosamine repeating units. These results indicate the severe impairment in the catabolism of glycoconjugates with beta-linked galactose in type I, although this impairment is not as pronounced in type II.