keratan-sulfate and Gangliosidosis--GM1

G(M1)-gangliosidosis and Morquio B are rare lysosomal storage diseases associated with a neurodegenerative disorder or dwarfism and skeletal abnormalities, respectively. These diseases are caused by deficiencies in the lysosomal enzyme human β-D-galactosidase (h-β-GAL), which lead to accumulations of the h-β-GAL substrates, G(M1) ganglioside and keratan sulfate due to mutations in the h-β-GAL gene. H-β-GAL is an exoglycosidase that catalyzes the hydrolysis of terminal β-linked galactose residues. Here, we present the crystal structures of h-β-GAL in complex with its catalytic product galactose or with its inhibitor 1-deoxygalactonojirimycin. H-β-GAL showed a novel homodimer structure; each monomer was comprised of a catalytic TIM barrel domain followed by β-domain 1 and β-domain 2. The long loop region connecting the TIM barrel domain with β-domain 1 was responsible for the dimerization. To gain structural insight into the molecular defects of h-β-GAL in the above diseases, the disease-causing mutations were mapped onto the three-dimensional structure. Finally, the possible causes of the diseases are discussed.

Topics: Animals; beta-Galactosidase; Gangliosides; Gangliosidosis, GM1; Humans; Keratan Sulfate; Lysosomal Storage Diseases; Lysosomes; Molecular Conformation; Mucopolysaccharidosis IV; Mutation; Protein Structure, Tertiary; Substrate Specificity

Topics: Age of Onset; beta-Galactosidase; Bone Diseases, Developmental; Bone Marrow Examination; Diagnosis, Differential; Facial Bones; Female; Gangliosidosis, GM1; Glycosaminoglycans; Humans; Infant; Keratan Sulfate; Kyphosis; Leukocytes; Mucolipidoses; Mucopolysaccharidosis I; Mucopolysaccharidosis IV; Odontoid Process; Pedigree; Scoliosis

G(M1) gangliosidosis and Morquio B are autosomal recessive lysosomal storage diseases associated with a neurodegenerative disorder or dwarfism and skeletal abnormalities, respectively. These diseases are caused by deficiencies in the lysosomal enzyme β-d-galactosidase (β-Gal), which lead to accumulations of the β-Gal substrates, G(M1) ganglioside, and keratan sulfate. β-Gal is an exoglycosidase that catalyzes the hydrolysis of terminal β-linked galactose residues. This study shows the crystal structures of human β-Gal in complex with its catalytic product galactose or with its inhibitor 1-deoxygalactonojirimycin. Human β-Gal is composed of a catalytic TIM barrel domain followed by β-domain 1 and β-domain 2. To gain structural insight into the molecular defects of β-Gal in the above diseases, the disease-causing mutations were mapped onto the three-dimensional structure. Finally, the possible causes of the diseases are discussed.

Topics: 1-Deoxynojirimycin; beta-Galactosidase; Crystallography, X-Ray; G(M1) Ganglioside; Galactose; Gangliosidosis, GM1; Humans; Hydrolysis; Keratan Sulfate; Lysosomes; Models, Molecular; Mucopolysaccharidosis IV; Mutation; Protein Structure, Tertiary

G(M1)-gangliosidosis is a lysosomal storage disorder caused by acid beta-galactosidase deficiency. Aside from the lysosomal beta-galactosidase enzyme, the beta-galactosidase gene also encodes the elastin-binding protein (EBP), deficiency in which impairs elastogenesis. Using expression studies and Western blots of COS-1 cells, we identified and characterized four new and two known beta-galactosidase gene mutations detected in G(M1)-gangliosidosis patients with infantile, juvenile, or adult forms of disease. We then focused on impaired elastogenesis detected in fibroblasts from patients with infantile and juvenile disease. The juvenile patient showed connective-tissue abnormalities, unusual urinary keratan sulfate excretion, and an EBP reduction, despite mutations affecting only beta-galactosidase. Because galactosugar-bearing moieties may alter EBP function and impair elastogenesis, we assessed infantile and juvenile patients for the source of altered elastogenesis. We confirmed that the infantile patient's impaired elastogenesis arose from a primary EBP defect, according to molecular analysis. We examined the juvenile's fibroblasts by immunohistochemistry, addition of keratanase, soluble/insoluble elastin assay, and radiolabeling of tropoelastin. These experiments revealed that the juvenile's impaired elastogenesis likely arose from secondary EBP deficiency caused by keratan sulfate accumulation. Thus, impaired elastogenesis in G(M1)-gangliosidosis can arise from primary or secondary EBP defects in fibroblasts from infantile and juvenile patients, respectively.

Topics: Adolescent; Adult; Age of Onset; Amino Acid Sequence; Animals; Base Sequence; Child; Chlorocebus aethiops; Connective Tissue; COS Cells; DNA Primers; Elasticity; Exons; Face; Fibroblasts; Gangliosidosis, GM1; Humans; Infant; Keratan Sulfate; Mutation; Phenotype; Receptors, Cell Surface; Reverse Transcriptase Polymerase Chain Reaction; Transfection; Tropoelastin