Structure of a human lysosomal sulfatase.

BACKGROUND: . Sulfatases catalyze the hydrolysis of sulfuric acid esters from a wide variety of substrates including glycosaminoglycans, glycolipids and steroids. There is sufficient common sequence similarity within the class of sulfatase enzymes to indicate that they have a common structure. Deficiencies of specific lysosomal sulfatases that are involved in the degradation of glycosamino-glycans lead to rare inherited clinical disorders termed mucopolysaccharidoses. In sufferers of multiple sulfatase deficiency, all sulfatases are inactive because an essential post-translational modification of a specific active-site cysteine residue to oxo-alanine does not occur. Studies of this disorder have contributed to location and characterization of the sulfatase active site. To understand the catalytic mechanism of sulfatases, and ultimately the determinants of their substrate specificities, we have determined the structure of N-acetylgalactosamine-4-sulfatase. RESULTS: . The crystal structure of the enzyme has been solved and refined at 2.5 resolution using data recorded at both 123K and 273K. The structure has two domains, the larger of which belongs to the alpha/beta class of proteins and contains the active site. The enzyme active site in the crystals contains several hitherto undescribed features. The active-site cysteine residue, Cys91, is found as the sulfate derivative of the aldehyde species, oxo-alanine. The sulfate is bound to a previously undetected metal ion, which we have identified as calcium. The structure of a vanadate-inhibited form of the enzyme has also been solved, and this structure shows that vanadate has replaced sulfate in the active site and that the vanadate is covalently linked to the protein. Preliminary data is presented for crystals soaked in the monosaccharide N-acetylgalactosamine, the structure of which forms a product complex of the enzyme. CONCLUSIONS: . The structure of N-acetylgalactosamine-4-sulfatase reveals that residues conserved amongst the sulfatase family are involved in stabilizing the calcium ion and the sulfate ester in the active site. This suggests an archetypal fold for the family of sulfatases. A catalytic role is proposed for the post-translationally modified highly conserved cysteine residue. Despite a lack of any previously detectable sequence similarity to any protein of known structure, the large sulfatase domain that contains the active site closely resembles that of alkaline phosphatase: the calcium ion in sulfatase superposes on one of the zinc ions in alkaline phosphatase and the sulfate ester of Cys91 superposes on the phosphate ion found in the active site of alkaline phosphatase.

Targeted disruption of the arylsulfatase B gene results in mice resembling the phenotype of mucopolysaccharidosis VI.

Mucopolysaccharidosis VI (MPS VI) is a lysosomal storage disease with autosomal recessive inheritance caused by a deficiency of the enzyme arylsulfatase B (ASB), which is involved in degradation of dermatan sulfate and chondroitin 4-sulfate. A MPS VI mouse model was generated by targeted disruption of the ASB gene. Homozygous mutant animals exhibit ASB enzyme deficiency and elevated urinary secretion of dermatan sulfate. They develop progressive symptoms resembling those of MPS VI in humans. Around 4 weeks of age facial dysmorphia becomes overt, long bones are shortened, and pelvic and costal abnormalities are observed. Major alterations in bone formation with perturbed cartilaginous tissues in newborns and widened, perturbed, and persisting growth plates in adult animals are seen. All major parenchymal organs show storage of glycosaminoglycans preferentially in interstitial cells and macrophages. Affected mice are fertile and mortality is not elevated up to 15 months of age. This mouse model will be a valuable tool for studying pathogenesis of MPS VI and may help to evaluate therapeutical approaches for lysosomal storage diseases.

Preliminary molecular analysis of a case of feline mucopolysaccharidosis VI.

Deficiency of the lysosomal enzyme arylsulphatase B (ASB) causes, in man, the Maroteaux-Lamy disease (mucopolysaccharidosis type VI, MPS VI). MPS VI has been described also in Siamese cats. Isolation and characterization of the human and feline cDNAs encoding ASB has been reported as well as the assignment of the feline ASB gene to feline chromosome A1. The present paper describes the Southern and Northern blot analyses on DNA and RNA from an MPS VI affected cat using the human arylsulphatase B probe (ASB2). Our data suggest that a gross deletion/rearrangement of the ASB gene is present in the affected animal.

Lysosomal sulfate efflux following glycosaminoglycan degradation: measurements in enzyme-supplemented Maroteaux-Lamy syndrome fibroblasts and isolated lysosomes.

Studies using lysosomal membrane vesicles have suggested that efflux of the sulfate that results from lysosomal glycosaminoglycan degradation is carrier-mediated. In this study, glycosaminoglycan degradation and sulfate efflux were examined using cultured skin fibroblasts and lysosomes deficient in the lysosomal enzyme N-acetylgalactosamine-4-sulfatase. Such fibroblasts store dermatan sulfate lysosomally, which could be labelled biosynthetically with Na2(35)SO4. The addition of recombinant N-acetylgalactosamine-4-sulfatase to the media of 35S labelled fibroblasts degraded up to 82% of the stored dermatan [35S] sulfate over a subsequent 96 h chase and released inorganic [35S] sulfate into the medium. In the presence of 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid (SITS), sulfate was reused to a minor extent in newly synthesized proteoglycan. Isolated granules from recombinant enzyme supplemented fibroblasts degraded stored dermatan [35S]sulfate to sulfate which was rapidly released into the medium at a rate that was reduced by the extra-lysosomal presence of the lysosomal sulfate transport inhibitors SITS, Na2SO4 and Na2MoO4. SITS also inhibited dermatan sulfate turnover, although it had no effect on the action of purified recombinant enzyme in vitro. These data imply that sulfate clearance occurred concomitantly with dermatan sulfate turnover in the lysosome even at high substrate loading, and that lysosome-derived sulfate, while available, is reutilized minimally in synthetic pathways.

Pathological characteristics of mucopolysaccharidosis VI in the rat.

The histological and electron microscopical characteristics of the pathology of rats with arylsulphatase B-deficient mucopolysaccharidosis (mucopolysaccharidosis VI; MPS VI) were investigated. In affected animals, intracytoplasmic vacuoles were prominent in chondrocytes, the macrophage system, cardiac valve fibroblasts, cornea, connective tissues, vascular smooth muscle cells and uterine stromal cells. Tissues containing glucosaminoglycans stored in lysosomes were positive to Mowry's colloidal iron and alcian blue stains. By electron microscopy, the lysosomes were seen to be distended by electron lucent or fine fibrillary storage material, and lysosomal storage was also detected in the endothelial cells of the arteries and cornea. In the central and peripheral nervous system abnormalities were restricted to the connective tissue. Lesions in the affected rats resembled those described in human and feline mucopolysaccharidosis VI. These results indicate that MPS VI of the rat may be a useful animal model for human MPS VI (Maroteaux-Lamy syndrome).

Arylsulfatase B-deficient mucopolysaccharidosis in rats.

A rat colony with mucopolysaccharidosis VI was established and the clinical, pathological, and biochemical features were characterized. Affected rats had facial dysmorphia, dysostosis multiplex, and increased urinary excretion of glucosaminoglycans (GAGs). Ultrastructural studies revealed storage of GAGs throughout the reticuloendothelial cells, cartilage, and other connective tissues, but no deposition was observed in the nervous system. Biochemical analyses demonstrated that the excreted GAG was dermatan sulfate and the activity of hepatic arylsulfatase B was < 5% of the normal mean value. Pedigree analysis showed that the phenotype was inherited as an autosomal recessive single trait. The availability of a rat model of human mucopolysaccharidosis VI should permit the development and evaluation of various strategies to treat the human disease.

Correction of human mucopolysaccharidosis type-VI fibroblasts with recombinant N-acetylgalactosamine-4-sulphatase.

A full-length human N-acetylgalactosamine-4-sulphatase (4-sulphatase) cDNA clone was constructed and expressed in CHO-DK1 cells under the transcriptional control of the Rous sarcoma virus long terminal repeat. A clonal cell line expressing high activities of human 4-sulphatase was isolated. The maturation and processing of the human enzyme in this transfected CHO cell line showed it to be identical with that seen in normal human skin fibroblasts. The high-uptake precursor form of the recombinant enzyme was purified from the medium of the transfected cells treated with NH4Cl and was shown to be efficiently endocytosed by control fibroblasts and by fibroblasts from a mucopolysaccharidosis type-VI (MPS VI) patient. Enzyme uptake was inhibitable by mannose 6-phosphate. After uptake, the enzyme was processed normally in both normal and MPS VI fibroblasts and was shown both to correct the enzymic defect and to initiate degradation of [35S]sulphated dermatan sulphate in MPS VI fibroblasts. The stabilities of the recombinant enzyme and enzyme from human fibroblasts appeared to be similar after uptake. However, endocytosed enzyme has a significantly shorter half-life than endogenous human enzyme. The purified precursor 4-sulphatase had a similar pH optimum and catalytic parameters to the mature form of 4-sulphatase isolated from human liver.

Multiple sulfatase deficiency: catalytically inactive sulfatases are expressed from retrovirally introduced sulfatase cDNAs.

Multiple sulfatase deficiency (MSD) is an inherited lysosomal storage disease characterized by the deficiency of at least seven sulfatases. The basic defect in MSD is thought to be in a post-translational modification common to all sulfatases. In accordance with this concept, RNAs of normal size and amount were detected in MSD fibroblasts for three sulfatases tested. cDNAs encoding arylsulfatase A, arylsulfatase B, or steroid sulfatase were introduced into MSD fibroblasts and fibroblasts with a single sulfatase deficiency by retroviral gene transfer. Infected fibroblasts overexpressed the respective sulfatase polypeptides. While in single-sulfatase-deficiency fibroblasts a concomitant increase of sulfatase activities was observed, MSD fibroblasts expressed sulfatase polypeptides with a severely diminished catalytic activity. From these results we conclude that the mutation in MSD severely decreases the capacity of a co- or post-translational process that renders sulfatases enzymatically active or prevents their premature inactivation.

An N-acetylgalactosamine-4-sulfatase mutation (delta G238) results in a severe Maroteaux-Lamy phenotype.

Maroteaux-Lamy syndrome (mucopolysaccharidosis type VI, MPS VI) is an autosomally inherited lysosomal storage disorder caused by a deficiency of N-acetylgalactosamine-4-sulfatase (EC 3.1.6.1; 4-sulfatase). In order to determine the gene defect in a clinically severe MPS VI patient, polymerase chain reaction (PCR) products were generated from the patient's fibroblast mRNA and also from a 4-sulfatase cDNA clone and subjected to the chemical cleavage technique to detect mismatched bases, which were then identified by direct DNA sequencing of the PCR products. The patient was homozygous for an early frameshift mutation caused by the deletion of a G at position 238 (delta G238), which produces a truncated 4-sulfatase with an altered amino acid sequence from amino acid 80 to a premature stop codon at codon 113 relative to the normal 4-sulfatase reading frame of 533 amino acids. Since the mutation occurs only 40 amino acids past the signal peptidase cleavage site, it is most likely that this will result in a protein with no 4-sulfatase activity. This is consistent with the severe clinical presentation and the absence of 4-sulfatase enzyme activity or mutant 4-sulfatase protein in the patient. The patient was also found to be homozygous for two polymorphisms, i.e., a G to A transition at nucleotide 1072 resulting in a valine358 to methionine substitution (V358M) and a salient A to G transition in the third base of the proline397 codon at nucleotide 1191.

Animal models for lysosomal storage diseases: a new case of feline mucopolysaccharidosis VI.

Two long-haired Siamese cats are reported with clinical manifestations of human mucopolysaccharidosis VI (Maroteaux-Lamy disease): facial dysmorphia, dysostosis multiplex, paralysis. Urine of the two affected animals contained a high concentration of glycosaminoglycans, as detected by the dimethylmethylene blue test. Qualitative analysis, performed by thin-layer chromatography of the cetylpyridinium chloride-precipitable material, showed dermatan sulphate. Excessive incorporation of [35S]sulphate in the intracellular mucopolysaccharide of cultured fibroblasts and deficiency of arylsulphatase B in such cells indicate that these cats are affected by Maroteaux-Lamy disease. They should thus be considered the first European case of feline mucopolysaccharidosis VI.

Normal MPS excretion, but dermatan sulphaturia, combined with a mild Maroteaux-Lamy phenotype.

A mildly affected Maroteaux-Lamy patient is described. Electrophoretic separation of acid mucopolysaccharides (MPS) in the urine showed an increased excretion of dermatan sulphate in spite of a normal total excretion of MPS.

Glycosaminoglycan and collagen metabolism in arylsulfatase B-deficient retinal pigment epithelium in vitro.

Regional differences in retinal pigment epithelial (RPE) cell glycosaminoglycan (GAG) and collagen metabolism were studied using cells obtained from normal cats and those with deficient activity of arylsulfatase B (ASB), a lysosomal enzyme involved in GAG catabolism. Control and ASB-deficient RPE cultures initiated from superior equatorial (superior) and inferior equatorial (inferior) regions of the eye were radiolabeled for 72 hr with 35SO4, and GAGs from the media and cell layers were analyzed separately. In ASB-deficient RPE, there was an accumulation of dermatan/chondroitin sulfate in the cell layer of cultures initiated from the superior region of the eye but not in those initiated from the inferior region. This agrees with previous in situ and in vitro morphologic observations that accumulation of inclusions in ASB-deficient RPE was greater in the superior region of the eye than in the inferior region. By contrast, media from ASB-deficient cultures initiated from the inferior region of the eye contained much higher levels of radiolabeled dermatan/chondroitin sulfate than ASB-deficient cultures from the superior region or normal cultures. Increased GAG content in the media may result from increased secretion of proteoglycans, increased turnover of cell surface or extracellular matrix components, or extrusion of lysosomal contents. These results indicate that one or more of these mechanisms vary regionally throughout the eye in the RPE of ASB-deficient animals. Collagen production was determined in normal and ASB-deficient RPE cultures. In normal RPE, no differences in collagen synthesis were noted between the inferior and superior regions.(ABSTRACT TRUNCATED AT 250 WORDS)

Multiple sulfatase deficiency.

Multiple sulfatase deficiency is an inherited disorder characterized by a deficiency of several sulfatases and the accumulation of sulfatides, glycosaminoglycans, sphingolipids, and steroid sulfates in tissues and body fluids. The clinical manifestations represent the summation of two diseases: late infantile metachromatic leukodystrophy and mucopolysaccharidosis. We present a 9-year-old girl with a phenotype similar to a mucopolysaccharidosis: short stature, microcephaly, and mild facial dysmorphism, along with dysphagia, retinal degeneration, developmental arrest, and ataxia. We discuss the importance of measuring the sulfatase activities in the leukocytes, and the instability of sulfatases in the cultured skin fibroblasts.

Mental retardation in a patient with Maroteaux-Lamy.

An 8-year-old boy with Hurler-like traits including severe mental retardation excreted in his urine a pathognomonic amount of dermatan sulfate. Less than 10% residual activity of arylsulfatase B was found in his leucocytes and fibroblasts. Hurler fibroblasts corrected an abnormally high 35SO4-incorporation into acid mucopolysaccharides (MPS) in cultured fibroblasts, whereas Maroteaux-Lamy fibroblasts did not. The patient thus has a rare combination of Maroteaux-Lamy and severe mental retardation.

Postnatal and prenatal diagnosis of Maroteaux-Lamy syndrome.

The clinical course up to 6 years of age is described in a boy with Maroteaux-Lamy syndrome as indicated by the clinical characteristics: increased urinary excretion of dermatan sulphate and deficiency of arylsulphatase B in leucocytes and cultured skin fibroblasts. A subsequent pregnancy of the mother was monitored by enzyme analysis of culture amniotic fluid cells. The prenatal diagnosis of an affected fetus was made and confirmed after termination of the pregnancy.

Correction of feline arylsulphatase B deficiency (mucopolysaccharidosis VI) by bone marrow transplantation.

Feline and human mucopolysaccharidosis VI (MPS VI or Maroteaux-Lamy syndrome) are inherited autosomal recessive deficiencies of lysosomal enzyme arylsulphatase B. Affected cats and children exhibit lesions caused by incompetent degradation, retinal atrophy and excessive urinary excretion of dermatan facial dysmorphia, corneal stromal opacities, leukocyte granulation, retinal atrophy and excessive urinary excretion of dermatan sulphate--and usually die before adulthood. Most attempts to treat humans affected with MPS VI or other mucopolysaccharidoses have been ineffective or logistically prohibitive, but allogeneic bone marrow transplantation (BMT) offers promise for cure of certain inborn errors of metabolism. Engraftment of normal donor marrow may endow the enzyme-deficient recipient with a continuous source of enzyme-competent blood cells and tissue macrophages to facilitate degradation of stored substrate and to prevent genesis of further malformations. To test this hypothesis, we performed allogeneic BMT in a 2-year-old male Siamese cat with advanced MPS VI. Here we describe BMT-induced correction of this hereditary enzyme deficiency.

Early manifestations of multiple sulfatase deficiency.

We describe two boys, presenting by 1 year of age, with developmental delay from birth, mildly coarse facial features, and hepatomegaly. These clinical features were most suggestive of a mucopolysaccharidosis, particularly MPS II. Biochemical studies, including sulfate incorporation in fibroblasts and lysosomal enzyme analyses in fibroblasts, leukocytes, and serum, showed abnormalities in both sulfatide and mucopolysaccharide metabolism and led to the diagnosis of multiple sulfatase deficiency. With time, both patients developed an ichthyotic rash and profound intellectual deterioration. We conclude that findings in the first year of life in some patients with MSD may closely resemble those in patients with a MPS disorder rather than the late infantile form of metachromatic leukodystrophy, as is classically described. Thus, MSD should be considered in the young patient suspected of having a MPS disorder.

Multiple sulphatase deficiency with early onset.

This male infant was first brought to attention in the neonatal period because he presented clinical and radiological evidence of multiple bone deformities. He was readmitted at 21/2 months for hydrocephaly, hepatosplenomegaly and poor somatic and psychomotor development. In addition, coarse facies, corneal opacities and stiff joints were noticed. Bone X-ray anomalies and vacuolized lymphocytes supported the clinical presumption of lysosomal storage disorder. The diagnosis of multiple sulphatase deficiency rests on the presence of MPS and sulphatides in the urine, the finding of a mixed storage process in conjunctival biopsy and the demonstration of deficiencies in arylsulphatases A, B, C, iduronate sulphatase and heparan sulphatase in serum, leukocytes and cultured fibroblasts.