Characterization of human alpha-galactosidase A and B before and after neuraminidase treatment

Human alpha-N-acetylgalactosaminidase: site occupancy and structure of N-linked oligosaccharides

Human alpha-N-acetylgalactosaminidase (alpha-GalNAc; also known as alpha-galactosidase B) is the lysosomal exoglycohydrolase that cleaves alpha-N-acetylgalactosaminyl moieties in glycoconjugates. Mutagenesis studies indicated that the first five (N124, N177, N201, N359, and N385) of the six potential N-glycosylation sites were occupied. Site 3 occupancy was important for enzyme function and stability. Characterization of the N-linked oligosaccharide structures on the secreted enzyme overexpressed in Chinese hamster ovary cells revealed highly heterogeneous structures consisting of complex (approximately 53%), hybrid (approximately 12%), and high mannose-type (approximately 33%) oligosaccharides. The complex structures were mono-, bi-, 2,4-tri-, 2,6-tri-, and tetraantennary, among which the biantennary structures were most predominant (approximately 53%). Approximately 80% of the complex oligo-saccharides had a core-region fucose and 50% of the complex oligosaccharides were sialylated exclusively with alpha-2,3-linked sialic acid residues. The majority of hybrid type oligo-saccharides were GalGlcNAcMan(6)GlcNAc-Fuc(0-1)GlcNAc. Approximately 54% of the hybrid oligosaccharide were phosphorylated and one-third of these structures were further sialylated, the latter representing unique phosphorylated and sialylated structures. Of the high mannose oligosaccharides, Man(5-7)GlcNAc(2) were the predominant species (approximately 90%) and about 50% of the high mannose oligosaccharides were phosphorylated, exclusively as monoesters whose positions were determined. Comparison of the oligosaccharide structures of alpha-GalNAc and alpha-galactosidase A, an evolutionary-related and highly homologous exoglycosidase, indicated that alpha-GalNAc had more completed complex chains, presumably due to differences in enzyme structure/domains, rate of biosynthesis, and/or aggregation of the overexpressed recombinant enzymes.

Structural organization and complete sequence of the human alpha-N-acetylgalactosaminidase gene: homology with the alpha-galactosidase A gene provides evidence for evolution from a common ancestral gene

Human alpha-N-acetylgalactosaminidase (alpha-GalNAc; EC 3.2.1.49), the lysosomal glycohydrolase that cleaves alpha-N-acetylgalactosaminyl moieties in glycoconjugates, is encoded by a gene localized to chromosome 22q13----qter. The deficient activity of this enzyme results in Schindler disease, an autosomal recessive disorder characterized by the increased urinary excretion of glycopeptides and oligosaccharides containing alpha-N-acetylgalactosaminyl moieties. Recently, the 3.6-kb full-length alpha-GalNAc cDNA sequence was isolated and found to have remarkable nucleotide and predicted amino acid homology (55.8 and 46.9%, respectively) with the human alpha-galactosidase A (alpha-Gal A) cDNA. To investigate the possible evolutionary relatedness of the two glycosidases, the alpha-GalNAc chromosomal gene was isolated and characterized. Screening of a human genomic DNA cosmid library resulted in the identification of a clone, gAGB-1, with an approximately 35-kb insert that contained the entire alpha-GalNAc gene. A single approximately 15-kb EcoRI fragment of gAGB-1, which contained the complete 3.6-kb cDNA sequence, was digested and the subcloned fragments were sequenced in both orientations. The 13,709-bp alpha-GalNAc gene had nine exons ranging from 95 to 2028 bp and intronic sequences of 304 to 2684 bp. All exon/intron junctions conformed to the GT/AG consensus rule. Analysis of 1.4 kb of 5' flanking sequence revealed three Sp1 and two CAAT-like promoter elements. This region was GC-rich (56%), but no HTF island was identified. The gene contained six Alu-repetitive elements, all in the reverse orientation. Comparison of the structural organization of the alpha-GalNAc and the alpha-Gal A genes revealed that all six alpha-Gal A introns were identically positioned in the homologous alpha-GalNAc exonic sequence. Two additional introns, 1 and 8, were identfied in the alpha-GalNAc gene. The predicted amino acid sequences of alpha-GalNAc exons 2 through 7 and those of corresponding alpha-Gal A exons 1 through 6 were 46.2 to 62.7% identical. In contrast, there was little, if any, similarity between the deduced amino acid sequences of alpha-Gal A exon 7 and alpha-GalNAc exons 8 and 9. The remarkable amino acid identity and the identical exonic interruption by six introns of the alpha-GalNAc and alpha-Gal A genes suggest that this region in both genes is evolutionarily related and arose through duplication and divergence from a common ancestral gene.

Plasma alpha-galactosidase A:properties and comparisons with tissue alpha-galactosidases

The human plasma form of alpha-galactosidase A (alpha-D-galactoside galactohydrolase, EC 3.2.1.22) was highly purified and exhibited apparent Km values of 1.9 mM with 4-methylumbelliferyl-alpha-D-galactopyranoside and 0.23 mM with globotriglycosylceramide. Its inhibition with myo-inositol (Ki = 0.29 M) was similar to that observed with alpha-galactosidase A from various tissues. The plasma form of this lysosomal enzyme has a lower molecular weight of 96 600, a lower pI of 3.7 and faster electrophoretic mobility in polyacrylamide gels than the enzyme obtained from human liver. These data and the increased pI obtained after neuraminidase treatment suggest that the plasma form is an isoenzyme with a more highly sialylated carbohydrate moiety than the tissue isoenzymes.

Pilot scale purification of alpha-galactosidase A from Cohn fraction IV-1 of human plasma

Human plasma alpha-galactosidase A (alpha-D-galactoside galactohydrolase, EC 3.2.1.22) was purified 7000-fold over plasma levels from Cohn Fraction IV-1. The yield per kg starting material averaged 11 000 units (nmol galactose liberated per h) and the specific activity was about 600 units per mg protein with 4-methylumbelliferyl-alpha-D-galactoside. The ratio of 4-methylumbelliferyl-alpha-galactosidase to ceramide trihexosidase activities was 6.2. Both activities were heat labile and exhibited the same relative mobilities on polyacrylamide gel electrophoresis. Enzymatic activity was stable for at least 4 months at 4 and -20 degrees C. The endotoxin concentration of this preparation averaged 0.26 mg per mg protein.

Glycosphingolipid hydrolases: properties and molecular genetics

This is a review of the properties and molecular genetics of six lysosomal hydrolases: beta-galactosidase, hexosaminidases A and B, alpha-galactosidase, beta-glucosidase and alpha-fucosidase. Each enzyme is discussed with regards to isoenzymes and substrate specificity, subunit structure, genetic relationship of isoenzymes and genetic variants. The molecular genetics of human diseases caused by deficiencies of each enzyme are discussed.

Enzymological properties and immunological characterization of alpha-galactosidase isoenzymes from normal and Fabry human liver

1. A method is described for the rapid isolation of alpha-galactosidases A and B (alpha-D-galactoside galactohydrolase, EC 3.2.1.22) from normal human liver. 2. When the same method is applied to Fabry liver, most of the alpha-galactosidase activity is recovered in the fraction corresponding to normal alpha-galactosidase B. In agreement with Romeo, G., D'Urso, M., Pisacane, A., Blum, E., De Falco, A. and Ruffilli, A. (1975) Biochem. Genet. 13, 615-628) [18], a small amount of alpha-galactosidase activity is found in the fraction corresponding to normal alpha-galactosidase A. 3. The kinetic properties of the B-like activity from Fabry liver are similar to those of normal alpha-galactosidase B. In agreement with Romeo et al. [18], it was found that the kinetic properties of the A-like activity from Fabry liver are similar to those of normal alpha-galactosidase A. 4. Using antisera raised against normal alpha-galactosidase A and normal alpha-galactosidase B, it is shown that the normal alpha-galactosidase isoenzymes are immunologically distinct and that the B-like activity from Fabry liver is immunologically related to normal alpha-galactosidase B. Furthermore, the A-like activity from Fabry liver is immunologically related to normal alpha-galactosidase B and not to normal alpha-galactosidase A. 5. Normal alpha-galactosidase B is converted into an A-like form during storage. 6. It is concluded that the B-like alpha-galactosidase in Fabry tissues is identical to normal alpha-galactosidase B, and that the small amount of A-like activity found in Fabry material is due to a modified form of alpha-galactosidase B.

Human alpha-fucosidase. Single residual enzymatic form in fucosidosis

Four major forms of alpha-fucosidase (EC 3.2.1.51) activity were separated by isoelectrofocusing from sera of normal control individuals. All forms shifted towards less acidic pI values after neuraminidase treatment. In two patients affected with fucosidosis, only a single major acidic peak was observed and this was affected to a lesser degree by neuraminidase treatment. The kinetics of heat inactivation of the residual activity found in these two patients showed two decay rates while the controls showed only one rate. These data are considered in relation to the hypothesis of the existence of interconvertible thermolabile and thermostable forms of the enzyme which has been discussed in the preceeding paper. The residual alpha-fucosidase found in patients could be structurally altered so that its ability to form the thermostable higher molecular weight aggregates is impaired.

Human alpha-fucosidase. Purification and properties

Human placental alpha-fucosidase (EC 3.2.1.51) has been extensively purified and partially characterized with respect to kinetic and structured properties. Although the enzyme seems to be separated by DEAE-cellulose chromatography in two forms which differ in their molecular weight and thermostability, an interconversion between the two forms takes place during storage and/or electrofocusing so that the same peaks of activity, revealed by the latter technique, are found before and after DEAE-cellulose chrome. The heterogeneous peaks of activity revealed by isoelectrofocusing show a reproducible pattern in the different tissues examined, except in serum where their pI values are consistently more acidic.

Residual activity of alpha-galactosidase A in Fabry's disease

The alpha-galactosidase A activity from fibroblasts of five Fabry patients and five controls has been separated from alpha-galactosidase B through small DEAE-cellulose columns and in some experiments by treatment of the fibroblast extracts with Sepharose coupled to anti-alpha-galactosidase B antibodies. By these independent methods, it has been shown that there is a residual alpha-galactosidase A in Fabry's disease, which is immunologically similar to the alpha-galactosidase A from the controls. The alpha-galactosidase A from all of the patients and controls has the same apparent Km value for the synthetic substrate 4-methylumbelliferyl-alpha-galactosidase A, while the fifth has a thermolabile enzyme like that from the controls. The amount of immunologically active alpha-galactosidase A seems to be decreased in the patients tested.