Structure of a human lysosomal sulfatase

Lysophospholipid interactions with protein targets

Bioactive lysophospholipids include lysophosphatidic acid (LPA), sphingosine 1-phosphate (S1P), cyclic-phosphatidic acid (CPA) and alkyl glycerolphosphate (AGP). These lipid mediators stimulate a variety of responses that include cell survival, proliferation, migration, invasion, wound healing, and angiogenesis. Responses to lysophospholipids depend upon interactions with biomolecular targets in the G protein-coupled receptor (GPCR) and nuclear receptor families, as well as enzymes. Our current understanding of lysophospholipid interactions with these targets is based on a combination of lysophospholipid analog structure activity relationship studies as well as more direct structural characterization techniques such as X-ray crystallography, nuclear magnetic resonance (NMR) spectroscopy, and experimentally-validated molecular modeling. The direct structural characterization studies are the focus of this review, and provide the insight necessary to stimulate structure-based therapeutic lead discovery efforts in the future.

Genetic analysis of mucopolysaccharidosis type VI in Taiwanese patients

BACKGROUND

Mucopolysaccharidosis type VI (MPS VI; Maroteaux-Lamy syndrome) is an autosomal recessive lysosomal storage disease induced by a deficiency of the enzyme N-acetylgalactosamine-4-sulfatase (arylsulfatase B, ARSB). The deficiency of ARSB leads to an accumulation of dermatan sulfate (DS) in lysosomes and gross excretion in the urine. The prevalence of these mutations in Asian MPS VI patients has not yet been thoroughly investigated. We studied the ARSB gene profile of 9 Taiwanese MPS VI patients.

METHODS

To validate the patients' type of MPS, urine mucopolysaccharide was defined by 2-dimensional electrophoresis and leukocyte ARSB activity was determined by fluorogenic assay. Direct sequencing was used to identify any mutation in the patients' ARSB gene.

RESULTS

Abnormal excretion of DS and low leukocyte ARSB activity was observed in the urine samples of all 9 patients studied. A total of 8 mutations within the ARSB gene were revealed by molecular analysis. Four mutations, c.574T>C (p.Cys192Arg) and c.943C>T (p.Arg315Stop) mutations had been observed in other populations and c.716A>G (p.Gln239Arg) and c.1197C>G (p.Phe399Leu) were previously reported by our group. The other 4 mutations c.395T>C (p.Leu132Pro), c.908G>A (p.Gly303Glu), c.1228 C>A (p.His430Asn) and c.1394C>G (p.Ser465X), had not been reported before. The c.1197C>G (p.Phe399Leu) and c.395T>C (p.Leu132Pro) mutations were the most common missense mutation in the patients studied (8 in 18 mutant alleles). According to statistical data, the incidence of MPS VI in Taiwan is approximately 1 in 833,000 in live birth.

CONCLUSION

The ARSB gene mutation profile in Taiwanese MPS VI patients may be different from MPS VI patients from other countries.

Structural and clinical implications of amino acid substitutions in N-acetylgalactosamine-4-sulfatase: insight into mucopolysaccharidosis type VI

To elucidate the basis of mucopolysaccharidosis type VI (MPS VI) from the point of view of enzyme structure, we built structural models of mutant N-acetylgalactosamine-4-sulfatase (4S) resulting from 34 missense mutations (17 severe and 17 attenuated), and analyzed the influence of each amino acid replacement on the structure by calculating the number of atoms affected. Then, we calculated the average of solvent-accessible surface area value of the residues for which a substitution was identified in the severe MPS VI group and compared it with that in the attenuated MPS VI group. In the severe MPS VI group, the number of atoms influenced by a mutation was generally larger than that in the attenuated MPS VI group in both the main chain and the side chain, and residues associated with the mutations found in the severe MPS VI group tended to be less solvent-accessible than those in the attenuated MPS VI group. Furthermore, we analyzed the structural changes in 4S caused by six amino acid substitutions, for which the expressed proteins have been characterized, by means of color imaging. The results revealed that R95Q, G144R, H393P, and C521Y cause large structural changes, and that they are associated with the severe phenotype. On the other hand, G137V and Y210C are thought to cause small structural changes in a limited region resulting in the attenuated phenotype. Structural study is useful for elucidating the basis of MPS VI and predicting the influence of amino acid substitutions on clinical outcome, although there are a couple of exceptional cases.

A review of coumarin derivatives in pharmacotherapy of breast cancer

The coumarin (benzopyran-2-one, or chromen-2-one) ring system, present in natural products (such as the anticoagulant warfarin) that display interesting pharmacological properties, has intrigued chemists and medicinal chemists for decades to explore the natural coumarins or synthetic analogs for their applicability as drugs. Many molecules based on the coumarin ring system have been synthesized utilizing innovative synthetic techniques. The diversity oriented synthetic routes have led to interesting derivatives including the furanocoumarins, pyranocoumarins, and coumarin sulfamates (COUMATES), which have been found to be useful in photochemotherapy, antitumor and anti-HIV therapy, and as stimulants for central nervous system, antibacterials, anti-inflammatory, anti-coagulants, and dyes. Of particular interest in breast cancer chemotherapy, some coumarins and their active metabolite 7-hydroxycoumarin analogs have shown sulfatase and aromatase inhibitory activities. Coumarin based selective estrogen receptor modulators (SERMs) and coumarin-estrogen conjugates have also been described as potential antibreast cancer agents. Since breast cancer is the second leading cause of death in American women behind lung cancer, there is a strong impetus to identify potential new drug treatments for breast cancer. Therefore, the objective of this review is to focus on important coumarin analogs with antibreast cancer activities, highlight their mechanisms of action and structure-activity relationships on selected receptors in breast tissues, and the different methods that have been applied in the construction of these pharmacologically important coumarin analogs.

Inactivation of recombinant human steroid sulfatase by KW-2581

Steroid sulfatase (STS) catalyses the hydrolysis of the sulfate esters of 3-hydroxy steroids, which are inactive transport or precursor forms of the active 3-hydroxy steroids. STS inhibitors are expected to block the local production and, consequently to reduce the active steroid levels; therefore, they are considered as potential new therapeutic agents for the treatment of estrogen- and androgen-dependent disorders such as breast and prostate cancers. KW-2581 is a novel steroidal STS inhibitor. In the present study, we found KW-2581 inhibited recombinant human STS (rhSTS) activity with an IC(50) of 2.9 nM when estrone sulfate was used as a substrate. The potency of KW-2581 was approximately 5-fold higher than that of a non-steroidal STS inhibitor, 667 COUMATE. KW-2581 was able to equally inhibit rhSTS activity when dehydroepiandrosterone sulfate was used as another substrate. KW-2581 inhibited rhSTS activity in a time- and concentration-dependent manner (k(inact), 0.439 min(-1); K(i, app), 15 nM), suggesting that it is an active site-directed irreversible inhibitor. Both decrease of KW-2581 concentration and increase of the des-sulfamoylated form's concentration were simultaneously observed during the reaction in a time-dependent manner with corresponding to the decrease of STS activity. Our findings for the first time demonstrated the production of des-sulfamoylated form of the compound as a consequence of STS inactivation.

Genetic and functional analyses of PptA, a phospho-form transferase targeting type IV pili in Neisseria gonorrhoeae

The PilE pilin subunit protein of Neisseria gonorrhoeae undergoes unique covalent modifications with phosphoethanolamine (PE) and phosphocholine (PC). The pilin phospho-form transferase A (PptA) protein, required for these modifications, shows sequence relatedness with and architectural similarities to lipopolysaccharide PE transferases. Here, we used regulated expression and mutagenesis as means to better define the relationships between PptA structure and function, as well as to probe the mechanisms by which other factors impact the system. We show here that pptA expression is coupled at the level of transcription to its distal gene, murF, in a division/cell wall gene operon and that PptA can act in a dose-dependent fashion in PilE phospho-form modification. Molecular modeling and site-directed mutagenesis provided the first direct evidence that PptA is a member of the alkaline phosphatase superfamily of metalloenzymes with similar metal-binding sites and conserved structural folds. Through phylogenetic analyses and sequence alignments, these conclusions were extended to include the lipopolysaccharide PE transferases, including members of the disparate Lpt6 subfamily, and the MdoB family of phosphoglycerol transferases. Each of these enzymes thus likely acts as a phospholipid head group transferase whose catalytic mechanism involves a trans-esterification step generating a protein-phospho-form ester intermediate. Coexpression of PptA with PilE in Pseudomonas aeruginosa resulted in high levels of PE modification but was not sufficient for PC modification. This and other findings show that PptA-associated PC modification is governed by as-yet-undefined ancillary factors unique to N. gonorrhoeae.

Effect of 'attenuated' mutations in mucopolysaccharidosis IVA on molecular phenotypes of N-acetylgalactosamine-6-sulfate sulfatase

Mucopolysaccharidosis IVA is an autosomal recessive disease caused by the deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS). Mutation screening of the GALNS gene was performed for seven MPS IVA patients with attenuated phenotypes from three unrelated families. Four of 5 missense mutations identified in this study (p.F167V, p.R253W, p.R380S, p.P484S) and two reported (p.F97V, p.N204K), associated with attenuated phenotypes, were characterized using in vitro stable expression experiments, enzyme kinetic study, protein processing and structural analysis. The stably expressed mutant enzymes defining the attenuated phenotype exhibited a considerable residual activity (1.2-36.7% of the wild-type GALNS activity) except for p.R380S. Enzyme kinetic studies showed that p.F97V, p.F167V and p.N204K have lower affinity to the substrate compared with other mutants. The p.F97V enzyme was the most thermolabile at 55 degrees C. Immunoblot analyses indicated a rapid degradation and/or an insufficiency in processing in the mutant proteins. Tertiary structure analysis revealed that although there was a tendency for 'attenuated' mutant residues to be located on the surface of GALNS, they have a different effect on the protein including modification of the hydrophobic core and salt-bridge formation and different potential energy. This study demonstrates that 'attenuated' mutant enzymes are heterogeneous in molecular phenotypes, including biochemical properties and tertiary structure.

Identification of the molecular defects in Spanish and Argentinian mucopolysaccharidosis VI (Maroteaux-Lamy syndrome) patients, including 9 novel mutations

Maroteaux-Lamy syndrome, or mucopolysaccharidosis VI (MPS VI), is an autosomal recessive lysosomal storage disorder caused by a deficiency of N-acetylgalactosamine-4-sulfatase or arylsulfatase B (ARSB). We aimed to analyze the spectrum of mutations responsible for the disorder in Spanish and Argentinian patients, not previously studied. We identified all the ARSB mutant alleles, nine of them novel, in 12 Spanish and 4 Argentinian patients. The new changes were as follows: six missense mutations: c.245T>G [p.L82R], c.413A>G [p.Y138C], c.719C>T [p.S240F], c.922G>A [p.G308R], c.1340G>T [p.C447F] and c.1415T>C [p.L472P]; one nonsense mutation: c.966G>A [p.W322X]; and two intronic changes involving splice sites: c.1142+2T>A, in the donor splice site of intron 5, which promotes skipping of exon 5, and c.1143-1G>C, which disrupts the acceptor site of intron 5, resulting in skipping of exon 6. We also report 10 previously described mutations as well as several non-pathogenic polymorphisms. Haplotype analysis indicated a common origin for most of the mutations found more than once. Most of the patients were compound heterozygotes, whereas only four of them were homozygous. These observations confirm the broad allelic heterogeneity of the disease, with 19 different mutations in 16 patients. However, the two most frequent mutations, c.1143-1G>C and c.1143-8T>G, present in both populations, accounted for one-third of the mutant alleles in this group of patients.

Mutational analysis of 105 mucopolysaccharidosis type VI patients

Mucopolysaccharidosis type VI (MPS VI; Maroteaux-Lamy syndrome) is a lysosomal storage disorder caused by mutations in the N-acetylgalactosamine-4-sulfatase (arylsulfatase B, ARSB) gene. ARSB is a lysosomal enzyme involved in the degradation of the glycosaminoglycans (GAG) dermatan and chondroitin sulfate. ARSB mutations reduce enzyme function and GAG degradation, causing lysosomal storage and urinary excretion of these partially degraded substrates. Disease onset and rate of progression is variable, producing a spectrum of clinical presentation. In this study, 105 MPS VI patients-representing about 10% of the world MPS VI population-were studied for molecular genetic and biochemical parameters. Direct sequencing of patient genomic DNA was used to identify ARSB mutations. In total, 83 different disease-causing mutations were found, 62 of which were previously unknown. The novel sequence changes included: 38 missense mutations, five nonsense mutations, 11 deletions, one insertion, seven splice-site mutations, and four polymorphisms. ARSB mutant protein and residual activity were determined on fibroblast extracts for each patient. The identification of many novel mutations unique to individuals/their families highlighted the genetic heterogeneity of the disorder and provided an appropriate cohort to study the MPS VI phenotypic spectrum. This mutation analysis has identified a clear correlation between genotype and urinary GAG that can be used to predict clinical outcome.

ARSA gene mutations in five Chinese metachromatic leukodystrophy patients

The objective was to identify arylsulfatase A mutations, if any, in five Chinese patients with metachromatic leukodystrophy. This would be the first such study in China. All eight exons and exon-intron boundaries of the arylsulfatase A gene (ARSA) were amplified with polymerase chain reaction, which was followed by direct DNA sequencing. Patient 1 exhibited a homozygous mutation at c.954G>A (p.W318X) in exon 5. Patient 2 exhibited compound heterozygous mutations, identified as one allele with the c.862C>T (p.R288C) missense mutation in exon 5 and the other allele with the c.1338dupC frameshift mutation in exon 8. Patient 3 exhibited only a c.179_180dupCA frameshift mutation in exon 1 in one allele. Patients 4 and 5 exhibited identical compound heterozygous mutations, identified as one allele with the c.296G>T (p.G99V) missense mutation and the other allele with the c.251G>A (p.R84Q) missense mutation in exon 2. Six DNA variants of the arylsulfatase A gene were identified: two novel frameshift mutations (c.179_180dupCA and c.1338dupC), one known nonsense mutation (p.W318X), and three known missense mutations (p.R84Q, p.G99V, and p.R288C).

Mutational analysis of mucopolysaccharidosis type VI patients undergoing a phase II trial of enzyme replacement therapy

Mucopolysaccharidosis type VI (MPS VI; Maroteaux-Lamy syndrome) is a lysosomal storage disorder caused by mutations in the N-acetylgalactosamine-4-sulfatase (ARSB) gene. These mutations result in a deficiency of ARSB activity. Ten MPS VI patients were involved in a phase II clinical study of enzyme replacement therapy. Direct sequencing of genomic DNA from these patients was used to identify ARSB mutations. Each individual exon of the ARSB gene was amplified by PCR and subsequently sequenced. Thirteen substitutions (c.215T>G [p.L72R] c.284G>A [p.R95Q], c.305G>A [p.R102H], c.323G>T [p.G108V], c.389C>T [p.P130L], c.511G>A [p.G171S], c.904G>A [p.G302R], c.944G>A [p.R315Q], c.1057T>C [p.W353R], c.1151G>A [p.S384N], c.1178A>C [p.H393P], c.1289A>G [p.H430R] and c.1336G>C [p.G446R]), one deletion (c.238delG), and two intronic mutations (c.1213+5G>A and c.1214-2A>G) were identified. Nine of the 16 mutations identified were novel (R102H, G108V, P130L, G171S, W353R, H430R, G446R, c.1213+5G>A and c.1214-2A>G). The two common polymorphisms c.1072G>A [p.V358M] and c.1126G>A [p.V376M] were identified in some of the patients, along with the silent mutations c.972A>G and c.1191A>G. Cultured fibroblast ARSB mutant protein and residual activity were determined for each patient and, together with genotype information, used to predict the expected clinical severity of each patient.

Increased arylsulfatase B activity in cystic fibrosis cells following correction of CFTR

BACKGROUND

The genetic disorder cystic fibrosis (CF) is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, impairing its function as a regulated anion channel involved with fluid secretion across epithelial cells. However, the clinical manifestations of CF are not thoroughly explained by impaired CFTR function. Experimental data have demonstrated oversulfation of glycoconjugates synthesized by CF epithelial cells of lung, pancreas, and other organs, and increases in the glycosaminoglycans dermatan sulfate and chondroitin sulfate in cultured skin fibroblasts from patients with CF. Since the enzyme arylsulfatase B (ASB) catalyzes hydrolysis of the sulfate ester of N-acetylgalactosamine 4-sulfate, a component of dermatan sulfate and chondroitin A sulfate, determination of ASB activity in human airway epithelial cells, corrected and uncorrected for CFTR, was undertaken.

METHODS

Arylsulfatase B (ASB) enzyme activity was measured in three pairs of cells in which the defect in CFTR was corrected or uncorrected. The substrates p-nitrocatechol sulfate and 4-MUS were used to measure activity.

RESULTS

An increase of 40% in ASB activity occurred in the CF cells when corrected for CFTR deficiency.

CONCLUSIONS

Decline in ASB activity may affect characteristics of secretions in CF, due to impaired metabolism of GAGs containing N-acetylgalactosamine 4-sulfate. ASB activity was markedly reduced when phosphate-buffered saline (PBS) was used as buffer, consistent with inhibition of sulfatase activity by phosphate. Increased attention to sulfatases may help to explain the pathophysiology of CF and lead to new therapies.

Down-regulation of messenger ribonucleic acid encoding an importer of sulfoconjugated steroids during human chorionic gonadotropin-induced follicular luteinization in vivo

Members of the organic anion transporting polypeptide (SLCO/OATP) superfamily are capable of importing anionic compounds across the lipid bilayer in a sodium-independent manner. Member 2B1 has been shown to transport few substrates, two of which are dihydroepiandrosterone-3-sulfate (DHEA-S) and estrone-3-sulfate. Steroid sulfatase (STS) catalyses the hydrolysis of these steroids into their unconjugated counterparts. The objective of this study was to investigate the regulation of SLCO2B1 and STS mRNAs during human chorionic gonadotropin (hCG)-induced ovulation/luteinization. The equine SLCO2B1 cDNA was cloned and shown to encode a 709-amino acid protein (OATP2B1) that is highly conserved when compared to mammalian orthologs. RT-PCR/Southern blot analyses were performed to study the regulation of SLCO2B1 and STS transcripts in equine preovulatory follicles isolated between 0 and 39h after hCG treatment. Results showed high levels of SLCO2B1 mRNA expression before hCG, with a marked decrease observed in follicles obtained 24-39h post-hCG (P<0.05). Analyses of isolated granulosa and theca interna cells identified high mRNA expression in both cell types prior to hCG treatment, with granulosa cells showing a more rapid SLCO2B1 mRNA down-regulation. No significant change in STS mRNA was observed in intact follicle walls. However, when both cell types were isolated, a significant decrease in STS mRNA was observed in granulosa cells 24-39h post-hCG. Collectively, these results demonstrate that the hCG-dependent induction of follicular luteinization is accompanied by the down-regulation of SLCO2B1 and STS transcripts. Considering that OATP2B1 can import sulfoconjugated DHEA and estrogens, and that STS can remove the sulfonate moiety from these steroids, their down-regulation in luteinizing preovulatory follicles may provide an additional biochemical basis for the decrease in ovarian 17beta-estradiol biosynthesis after the LH surge.

Steroid sulfatase, arylsulfatases A and B, galactose-6-sulfatase, and iduronate sulfatase in mammary cells and effects of sulfated and non-sulfated estrogens on sulfatase activity

Sulfatase enzymes have important roles in metabolism of steroid hormones and of glycosaminoglycans (GAGs). The activity of five sulfatase enzymes, including steroid sulfatase (STS; arylsulfatase C), arylsulfatase A (ASA; cerebroside sulfatase), arylsulfatase B (ASB; N-acetylgalactosamine-4-sulfatase), galactose-6-sulfatase (GALNS), and iduronate-2-sulfatase (IDS), was compared in six different mammary cell lines, including the malignant mammary cell lines MCF7, T47D, and HCC1937, the MCF10A cell line which is associated with fibrocystic disease, and in primary epithelial and myoepithelial cell lines established from reduction mammoplasty. The effects of estrogen hormones, including estrone, estradiol, estrone 3-sulfate, and estradiol sulfate on activity of these sulfatases were determined. The malignant cell lines MCF7 and T47D had markedly less activity of STS, ASB, ASA, and GAL6S, but not IDS. The primary myoepithelial cells had highest activity of STS and ASB, and the normal epithelial cells had highest activity of GALNS and ASA. Greater declines in sulfatase activity occurred in response to estrone and estradiol than sulfated estrogens. The study findings demonstrated marked variation in sulfatase activity and in effects of exogenous estrogens on sulfatase activity among the different mammary cell types.

Effect of Hunter disease (mucopolysaccharidosis type II) mutations on molecular phenotypes of iduronate-2-sulfatase: enzymatic activity, protein processing and structural analysis

Mucopolysaccharidosis II (Hunter disease), a lysosomal storage disorder caused by a deficiency of iduronate-2-sulfatase (IDS), has variable clinical phenotypes. Nearly 300 different mutations have been identified in the IDS gene from patients with Hunter disease, but the correlation between the genotype and phenotype has remained unclear. We studied the characteristics of 11 missense mutations, which were detected in the patients or artificially introduced, using stable expression experiments and structural analysis. The mutants found in the attenuated phenotype showed considerable residual activity (0.2-2.4% of the wild-type IDS activity) and those in the severe phenotype had no activity. In immunoblot analysis, both the 73-75 kDa precursor and processed forms were detected in the expression of 'attenuated' mutants (R48P, A85T and W337R) and the artificial active site mutants (C84S, C84T). The 73-75 kDa initial precursor was detected in the 'severe' mutants (P86L, S333L, S349I, R468Q, R468L). The truncated 68 kDa precursor form was synthesized in the Q531X mutant. The results of immunoblotting indicated rapid degradation and/or insufficiency in processing as a result of structural alteration of the IDS protein. A combination of analyses of genotype and molecular phenotypes, including enzyme activity, protein processing and structural analysis with an engineered reference protein, could provide an avenue to understanding the molecular mechanism of the disease and could give a useful tool for the evaluation of possible therapeutic chemical compounds.

Structure and molecular mechanism of Bacillus anthracis cofactor-independent phosphoglycerate mutase: a crucial enzyme for spores and growing cells of Bacillus species

Phosphoglycerate mutases (PGMs) catalyze the isomerization of 2- and 3-phosphoglycerates and are essential for glucose metabolism in most organisms. This study reports the production, structure, and molecular dynamics analysis of Bacillus anthracis cofactor-independent PGM (iPGM). The three-dimensional structure of B. anthracis PGM is composed of two structural and functional domains, the phosphatase and transferase. The structural relationship between these two domains is different than in the B. stearothermophilus iPGM structure determined previously. However, the structures of the two domains of B. anthracis iPGM show a high degree of similarity to those in B. stearothermophilus iPGM. The novel domain arrangement in B. anthracis iPGM and the dynamic property of these domains is directly linked to the mechanism of enzyme catalysis, in which substrate binding is proposed to result in close association of the two domains. The structure of B. anthracis iPGM and the molecular dynamics of this structure provide unique insight into the mechanism of iPGM catalysis, in particular the roles of changes in coordination geometry of the enzyme's two bivalent metal ions and the regulation of this enzyme's activity by changes in intracellular pH during spore formation and germination in Bacillus species.

Synthesis and evaluation of general mechanism-based inhibitors of sulfatases based on (difluoro)methyl phenyl sulfate and cyclic phenyl sulfamate motifs

Several model mechanism-based inhibitors (MbIs) were designed and evaluated for their ability to inhibit sulfatases. The MbI motifs were based on simple aromatic sulfates, which are known to be commonly accepted substrates across this highly conserved enzyme class, so that they might be generally useful for sulfatase labeling studies. (Difluoro)methyl phenol sulfate analogs, constructed to release a reactive quinone methide trap, were not capable of irreversibly inactivating the sulfatase active site. On the other hand, the cyclic sulfamates (CySAs) demonstrated inhibition profiles consistent with an active site-directed mode of action. These molecules represent a novel scaffold for labeling sulfatases and for probing their catalytic mechanism.

A New Type of Bacterial Sulfatase Reveals a Novel Maturation Pathway in Prokaryotes

Sulfatases are a highly conserved family of enzymes found in all three domains of life. To be active, sulfatases undergo a unique post-translational modification leading to the conversion of either a critical cysteine ("Cys-type" sulfatases) or a serine ("Ser-type" sulfatases) into a Calpha-formylglycine (FGly). This conversion depends on a strictly conserved sequence called "sulfatase signature" (C/S)XPXR. In a search for new enzymes from the human microbiota, we identified the first sulfatase from Firmicutes. Matrix-assisted laser desorption ionization time-of-flight analysis revealed that this enzyme undergoes conversion of its critical cysteine residue into FGly, even though it has a modified (C/S)XAXR sulfatase signature. Examination of the bacterial and archaeal genomes sequenced to date has identified many genes bearing this new motif, suggesting that the definition of the sulfatase signature should be expanded. Furthermore, we have also identified a new Cys-type sulfatase-maturating enzyme that catalyzes the conversion of cysteine into FGly, in anaerobic conditions, whereas the only enzyme reported so far to be able to catalyze this reaction is oxygen-dependent. The new enzyme belongs to the radical S-adenosyl-l-methionine enzyme superfamily and is related to the Ser-type sulfatase-maturating enzymes. This finding leads to the definition of a new enzyme family of sulfatase-maturating enzymes that we have named anSME (anaerobic sulfatase-maturating enzyme). This family includes enzymes able to maturate Cys-type as well as Ser-type sulfatases in anaerobic conditions. In conclusion, our results lead to a new scheme for the biochemistry of sulfatases maturation and suggest that the number of genes and bacterial species encoding sulfatase enzymes is currently underestimated.

Mutation and polymorphism spectrum of the GALNS gene in mucopolysaccharidosis IVA (Morquio A)

Mucopolysaccharidosis IVA (MPS IVA; Morquio A disease) is an autosomal-recessive disorder caused by a deficiency of lysosomal N-acetylgalactosamine-6-sulfate sulfatase (GALNS; E.C.3.1.6.4). GALNS is required to degrade glycosaminoglycans, keratan sulfate (KS), and chondroitin-6-sulfate. Accumulation of undegraded substrates in lysosomes of the affected tissues leads to a systemic bone dysplasia. We summarize information on 148 unique mutations determined to date in the GALNS gene, including 26 novel mutations (19 missense, four small deletions, one splice-site, and two insertions). This heterogeneity in GALNS gene mutations accounts for an extensive clinical variability within MPS IVA. Seven polymorphisms that cause an amino acid change, and nine silent variants in the coding region are also described. Of the analyzed mutant alleles, missense mutations accounted for 78.4%; small deletions, 9.2%; nonsense mutation, 5.0%; large deletion, 2.4%; and insertions, 1.6%. Transitional mutations at CpG dinucleotides accounted for 26.4% of all the described mutations. The importance of the relationship between methylation status and distribution of transitional mutations at CpG sites at the GALNS gene locus was elucidated. The three most frequent mutations (over 5% of all mutations) were represented by missense mutations (p.R386C, p.G301C, and p.I113F). A genotype/phenotype correlation was defined in some mutations. Missense mutations associated with a certain phenotype were studied for their effects on enzyme activity and stability, the levels of blood and urine KS, the location of mutations with regard to the tertiary structure, and the loci of the altered amino acid residues among sulfatase proteins.

Molecular cloning and initial characterization of three novel human sulfatases

Sulfatases constitute a group of enzymes capable of hydrolyzing the sulphate ester bond of a variety of biological compounds. To date, thirteen members of this family have been cloned and characterized as part of the human genome. In this work, the identification, molecular cloning and initial characterization of three new members of this human gene family is reported. Two map in chromosome 5 (5q15 and 5q32), whereas the third one maps in chromosome 4 (4q26). Two of them are closely related and are coded in only two exons, what is a unique genomic feature among the known sulfatases. The three new members were cloned from different DNA sources, and the predicted protein sizes range from 536 aa to 596 aa. Interestingly, initial characterization of two of them showed that their expression pattern was mainly restricted to embryonic tissues and some cancer cell lines.

Sulfatases and human disease

Sulfatases are a highly conserved family of proteins that cleave sulfate esters from a wide range of substrates. The importance of sulfatases in human metabolism is underscored by the presence of at least eight human monogenic diseases caused by the deficiency of individual sulfatases. Sulfatase activity requires a unique posttranslational modification, which is impaired in patients with multiple sulfatase deficiency (MSD) due to a mutation of the sulfatase modifying factor 1 (SUMF1). Here we review current knowledge and future perspectives on the evolution of the sulfatase gene family, on the role of these enzymes in human metabolism, and on new developments in the therapy of sulfatase deficiencies.

Structural characteristics of lysophosphatidic acid biological targets

Lysophosphatidic acid (LPA; 1-acyl-3-phosphoglycerol) exerts its biological activity through both extracellular and intracellular targets. Receptor targets include the cell-surface G-protein-coupled receptors LPA(1-4) and the nuclear PPAR-gamma (peroxisome-proliferator-activated receptor gamma). Enzyme targets include the secreted cancer cell motility factor, autotaxin, and the transmembrane phosphatases, LPP1-3 (where LPP stands for lipid phosphate phosphatase). Ion channel targets include the two pore domain ion channels in the TREK family, TREK-1, TREK-2 and TRAAK. Structural features of these targets and their interactions with LPA are reviewed.

Sulfatases and sulfatase modifying factors: an exclusive and promiscuous relationship

Sulfatases catalyze the hydrolysis of sulfate ester bonds from a wide variety of substrates. Several human inherited diseases are caused by the deficiency of individual sulfatases, while in patients with multiple sulfatase deficiency mutations in the Sulfatase Modifying Factor 1 (SUMF1) gene cause a defect in the post-translational modification of a cysteine residue into C(alpha)-formylglycine (FGly) at the active site of all sulfatases. This unique modification mechanism, which is required for catalytic activity, has been highly conserved during evolution. Here, we used a genomic approach to investigate the relationship between sulfatases and their modifying factors in humans and several model systems. First, we determined the complete catalog of human sulfatases, which comprises 17 members (versus 14 in rodents) including four novel ones (ARSH, ARSI, ARSJ and ARSK). Secondly, we showed that the active site, which is the target of the post-translational modification, is the most evolutionarily constrained region of sulfatases and shows intraspecies sequence convergence. Exhaustive sequence analyses of available proteomes indicate that sulfatases are the only likely targets of their modifying factors. Thirdly, we showed that sulfatases and ectonucleotide pyrophosphatases share significant homology at their active sites, suggesting a common evolutionary origin as well as similar catalytic mechanisms. Most importantly, gene association studies performed on prokaryotes suggested the presence of at least two additional mechanisms of cysteine-to-FGly conversion, which do not require SUMF1. These results may have important implications in the study of diseases caused by sulfatase deficiencies and in the development of therapeutic strategies.

Imperfect DNA mirror repeats in E. coli TnsA and other protein-coding DNA

DNA imperfect mirror repeats (DNA-IMRs) are ubiquitous in protein-coding DNA. However, they overlap and often have different centers of symmetry, making it difficult to evaluate their relationship to each other and to specific DNA and protein motifs and structures. This paper describes a systematic method of determining a hierarchy for DNA-IMRs and evaluates their relationship to protein structural elements (PSEs)--helices, turns and beta-sheets. DNA-IMRs are identifed by two different methods--DNA-IMRs terminated by reverse dinucleotides (rd-IMRs) and DNA-IMRs terminated by a single (mono) matching nucleotide (m-IMRs). Both rd-IMRs and m-IMRs are evaluated in 17 proteins, and illustrated in detail for TnsA. For each of the proteins, Fisher's exact test (FET) is used to measure the coincidence between the terminal dinucleotides of rd-IMRs and the terminal amino acids of individual PSEs. A significant correlation over a span of about 3 nt was found for each protein. The correlation is robust and for most genes, all rd-IMRs<or=13 nt can be removed without the loss of statistical significance. In TnsA, the protein intervals translated by rd-IMRs>16 nt contain approximately 88% of the potential functional motifs. The protein translation of the longest rd- and m-IMRs span sequences important to the protein's structure and function. In all 17 proteins studied, the population of rd-IMRs is substantially less than the expected number and the population of m-IMRs greater than the expected number, indicating strong selective pressures. The association of rd-IMRs with PSEs restricts their spatial distribution, and therefore, their number. The greater than predicted number of m-IMRs indicates that DNA symmetry exists throughout the entire protein-coding region and may stabilize the sequence.

Analysis of normal and mutant iduronate-2-sulphatase conformation

Mammalian sulphatases (EC 3.1.6) are a family of enzymes that have a high degree of similarity in amino acid sequence, structure and catalytic mechanism. IDS (iduronate-2-sulphatase; EC 3.1.6.13) is a lysosomal exo-sulphatase that belongs to this protein family and is involved in the degradation of the glycosaminoglycans heparan sulphate and dermatan sulphate. An IDS deficiency causes the lysosomal storage disorder MPS II (mucopolysaccharidosis type II). To examine the structural alterations in heat-denatured and mutant IDS, a panel of four monoclonal antibodies was raised to the denatured protein and used as probes of protein conformation. The linear sequence epitope reactivity of a polyclonal antibody raised against the native protein and the monoclonal antibodies were defined and mapped to distinct regions on the IDS protein. The antigenicity of native IDS was higher in regions without glycosylation, but reactivity was not restricted to protein surface epitopes. One monoclonal epitope was relatively surface accessible and in close proximity to an N-linked glycosylation site, while three others required additional thermal energy to expose the epitopes. The monoclonal antibodies demonstrated the capacity to differentiate progressive structural changes in IDS and could be used to characterize the severity of MPS type II in patients based on variable denatured microstates.

Molecular basis for multiple sulfatase deficiency and mechanism for formylglycine generation of the human formylglycine-generating enzyme

Sulfatases are enzymes essential for degradation and remodeling of sulfate esters. Formylglycine (FGly), the key catalytic residue in the active site, is unique to sulfatases. In higher eukaryotes, FGly is generated from a cysteine precursor by the FGly-generating enzyme (FGE). Inactivity of FGE results in multiple sulfatase deficiency (MSD), a fatal autosomal recessive syndrome. Based on the crystal structure, we report that FGE is a single-domain monomer with a surprising paucity of secondary structure and adopts a unique fold. The effect of all 18 missense mutations found in MSD patients is explained by the FGE structure, providing a molecular basis of MSD. The catalytic mechanism of FGly generation was elucidated by six high-resolution structures of FGE in different redox environments. The structures allow formulation of a novel oxygenase mechanism whereby FGE utilizes molecular oxygen to generate FGly via a cysteine sulfenic acid intermediate.

Steroid sulfatase: molecular biology, regulation, and inhibition

Steroid sulfatase (STS) is responsible for the hydrolysis of aryl and alkyl steroid sulfates and therefore has a pivotal role in regulating the formation of biologically active steroids. The enzyme is widely distributed throughout the body, and its action is implicated in physiological processes and pathological conditions. The crystal structure of the enzyme has been resolved, but relatively little is known about what regulates its expression or activity. Research into the control and inhibition of this enzyme has been stimulated by its important role in supporting the growth of hormone-dependent tumors of the breast and prostate. STS is responsible for the hydrolysis of estrone sulfate and dehydroepiandrosterone sulfate to estrone and dehydroepiandrosterone, respectively, both of which can be converted to steroids with estrogenic properties (i.e., estradiol and androstenediol) that can stimulate tumor growth. STS expression is increased in breast tumors and has prognostic significance. The role of STS in supporting tumor growth prompted the development of potent STS inhibitors. Several steroidal and nonsteroidal STS inhibitors are now available, with the irreversible type of inhibitor having a phenol sulfamate ester as its active pharmacophore. One such inhibitor, 667 COUMATE, has now entered a phase I trial in postmenopausal women with breast cancer. The skin is also an important site of STS activity, and deficiency of this enzyme is associated with X-linked ichthyosis. STS may also be involved in regulating part of the immune response and some aspects of cognitive function. The development of potent STS inhibitors will allow investigation of the role of this enzyme in physiological and pathological processes.

Overexpression of inactive arylsulphatase mutants and in vitro activation by light-dependent oxidation with vanadate

Arylsulphatases B (ASB) and A (ASA) are subject to a unique post-translational modification that is required for their function. The modification reaction, conversion of an active-site cysteine into a formylglycine, becomes saturated when these enzymes are overexpressed. We have removed the possibility of in vivo modification by expressing mutants of ASB and ASA in which the active-site cysteine is substituted with a serine. These mutants are expressed much more efficiently when compared with the native enzymes under identical conditions. The purified ASB mutant can then be converted into catalytically active ASB in vitro using vanadate and light.

Three‐Dimensional Structures of Sulfatases

The sulfatase family of enzymes catalyzes the hydrolysis of sulfate ester bonds of a wide variety of substrates. Nine human sulfatase proteins and their genes have been identified, many of which are associated with genetic disorders leading to reduction or loss of function of the corresponding enzyme. A catalytic cysteine residue, strictly conserved in prokaryotic and eukaryotic sulfatases, is modified posttranslationally into a formylglycine. Hydroxylation of the formylglycine residue by a water molecule forming the activated hydroxylformylglycine (a formylglycine hydrate or a gem-diol) is a necessary step for sulfatase activity of the enzyme. Crystal structures of three human sulfatases, arylsulfatases A and B (ARSA and ARSB) and C, also known as steroid sulfatase or estrone/dehydroepiandrosterone sulfatase (ES), have been determined. In addition, the crystal structure of a homologous bacterial arylsulfatase from Pseudomonas aeruginosa (PAS) is also available. While ARSA, ARSB, and PAS are water-soluble enzymes, ES has a hydrophobic domain and is presumed to be bound to the endoplasmic reticulum membrane. This chapter compares and contrasts four sulfatase structures and revisits the proposed catalytic mechanism in light of available structural and functional data. Examination of the ES active site reveals substrate-specific interactions previously identified in another steroidogenic enzyme. Possible influence of the lipid bilayer in substrate capture and recognition by ES is described. Finally, mapping the genetic mutations into the ES structure provides an explanation for the loss of enzyme function in X-linked ichthyosis.

Sulfatases: Structure, Mechanism, Biological Activity, Inhibition, and Synthetic Utility

Sulfatases, which cleave sulfate esters in biological systems, play a key role in regulating the sulfation states that determine the function of many physiological molecules. Sulfatase substrates range from small cytosolic steroids, such as estrogen sulfate, to complex cell-surface carbohydrates, such as the glycosaminoglycans. The transformation of these molecules has been linked with important cellular functions, including hormone regulation, cellular degradation, and modulation of signaling pathways. Sulfatases have also been implicated in the onset of various pathophysiological conditions, including hormone-dependent cancers, lysosomal storage disorders, developmental abnormalities, and bacterial pathogenesis. These findings have increased interest in sulfatases and in targeting them for therapeutic endeavors. Although numerous sulfatases have been identified, the wide scope of their biological activity is only beginning to emerge. Herein, accounts of the diversity and growing biological relevance of sulfatases are provided along with an overview of the current understanding of sulfatase structure, mechanism, and inhibition.

Expression and functional characterization of human mutant sulfamidase in insect cells

Mucopolysaccharidosis IIIA (MPS IIIA; Sanfilippo syndrome) is an autosomal recessive lysosomal disorder caused by the deficiency of sulfamidase (EC 3.10.1.1), required for the degradation of the mucopolysaccharide heparan sulfate. The molecular defects of 26 unrelated Spanish MPS IIIA patients were recently reported by our group. Here we describe the heterologous expression, using a baculovirus system, of the cDNAs corresponding to eight out of the 14 mutant alleles present in this patient group and the characterization of the corresponding mutant enzymes. In particular, we expressed the following alleles: p.S66W, p.R74H, p.Q85R, p.R206P, p.L386R, p.R433W, p.R433Q, and c.1079delC (previously named as c.1091delC), and the two variants of the polymorphism p.R456H. The expression of the mutant alleles and the characterization of the corresponding enzymes revealed that their activity was severely compromised. Only mutations p.S66W and p.R206P retained low levels of residual activity. However, Western blot analysis showed in all cases the presence of the expected two forms of the sulfamidase, the precursor and the mature proteins, indicating a normal processing of the mutant enzyme.

Identification and biochemical characterization of an avian sulfatase homologous to the human ARSE, the gene for X-linked chondrodysplasia punctata

Despite many efforts, the mouse homolog of ARSE, the gene implicated in X-linked recessive chondrodysplasia punctata, has not yet been identified. This absence has so far impaired a deep study of the role of this gene. For this reason, we searched the avian homolog and here report the identification of a chicken sulfatase, cARS, that shares high degree of homology with the cluster of sulfatases located on the short arm of the human X chromosome. cARS activity against a sulfated artificial substrate is heat labile and inhibited by warfarin, features that are characteristic of ARSE. The expression in pharyngeal arches, somites, and leg buds during chick development is consistent with cARS being the functional ortholog of ARSE, matching the tissues affected in this genetic disorder. The identification of the ARSE chicken gene is an important step for the study of its natural substrate and its role during development.

Enzyme-replacement therapy from birth delays the development of behavior and learning problems in mucopolysaccharidosis type IIIA mice

Mucopolysaccharidosis type IIIA (MPS IIIA; Sanfilippo syndrome) is a lysosomal storage disorder characterized by severe CNS degeneration, resulting in behavioral abnormalities and loss of learned abilities. Early treatment is vital to prevent long-term clinical pathology in lysosomal storage disorders. We have used naturally occurring MPS IIIA mice to assess the effects of long-term enzyme-replacement therapy initiated either at birth or at 6 wk of age. MPS IIIA and normal control mice received weekly i.v. injections of 1 mg/kg recombinant human sulfamidase until 20 wk of age. Sulfamidase is able to enter the brain until the blood-brain barrier completely closes at 10-14 d of age. MPS IIIA mice that were treated from birth demonstrated normal weight, behavioral characteristics, and ability to learn. MPS IIIA mice that were treated from birth performed significantly better in the Morris water maze than MPS IIIA mice that were treated from 6 wk of age or left untreated. A reduction in storage vacuoles in cells of the CNS in MPS IIIA mice that were treated from birth is consistent with the improvements observed. These data suggest that enzyme that enters the brain in the first few weeks of life, before the blood-brain barrier matures, is able to delay the development of behavior and learning difficulties in MPS IIIA mice.

The difluoromethylene group as a replacement for the labile oxygen in steroid sulfates: a new approach to steroid sulfatase inhibitors

Several estrone sulfate and estradiol sulfate analogues, in which the sulfate group was replaced with an alpha,alpha-difluoromethylenesulfonate group or an alpha,alpha-difluoromethylenetetrazole group, were examined as inhibitors of steroid sulfatase (STS). These compounds were 4.5-10.5 times more potent than their non-fluorinated analogues. Moreover, the presence of the fluorines changed the mode of inhibition from mixed to competitive. The inhibitor bearing the alpha,alpha-difluoromethylenetetrazole group exhibited an affinity for STS approaching that of the natural STS substrate, estrone sulfate. Possible reasons for the enhanced affinity of the fluorinated compounds compared to their non-fluorinated counterparts are discussed.

Recognition of arylsulfatase A and B by the UDP-N-acetylglucosamine:lysosomal enzyme N-acetylglucosamine-phosphotransferase

The critical step for sorting of lysosomal enzymes is the recognition by a Golgi-located phosphotransferase. The topogenic structure common to all lysosomal enzymes essential for this recognition is still not well defined, except that lysine residues seem to play a critical role. Here we have substituted surface-located lysine residues of lysosomal arylsulfatases A and B. In lysosomal arylsulfatase A only substitution of lysine residue 457 caused a reduction of phosphorylation to 33% and increased secretion of the mutant enzyme. In contrast to critical lysines in various other lysosomal enzymes, lysine 457 is not located in an unstructured loop region but in a helix. It is not strictly conserved among six homologous lysosomal sulfatases. Based on three-dimensional structure comparison, lysines 497 and 507 in arylsulfatase B are in a similar position as lysine 457 of arylsulfatase A. Also, the position of oligosaccharide side chains phosphorylated in arylsulfatase A is similar in arylsulfatase B. Despite the high degree of structural homology between these two sulfatases substitution of lysines 497 and 507 in arylsulfatase B has no effect on the sorting and phosphorylation of this sulfatase. Thus, highly homologous lysosomal arylsulfatases A and B did not develop a single conserved phosphotransferase recognition signal, demonstrating the high variability of this signal even in evolutionary closely related enzymes.

Crystal structure of a covalent intermediate of endogenous human arylsulfatase A

The structures of human arylsulfatase A crystals soaked in solutions containing 4-methylumbelliferyl phosphate and O-phospho-DL-tyrosine have been determined at 2.7- and 3.2-A resolution, respectively. The formylglycine in position 69, a residue crucial for catalytic activity, was unambiguously identified in both structures as forming a covalent bond to the phosphate moiety. A hydroxyl group is present at the Cbeta of residue 69 and the formation of one out of two possible stereomeric forms is strongly favoured. The structures confirm the importance of the gem-diol intermediate in the arylsulfatase's catalytic mechanism. The presence of an apparently stable covalent bond is consistent with the weak phosphatase activity observed for human arylsulfatase A. The structures of the complexes suggest that phosphate ions and phosphate esters inhibit arylsulfatase in non-covalent and covalent modes, respectively. The metal ion present in the active site of arylsulfatase A isolated from human placenta is Ca(2+) and not Mg(2+) as was found in the structure of the recombinant enzyme.

Structure of human estrone sulfatase suggests functional roles of membrane association

Estrone sulfatase (ES; 562 amino acids), one of the key enzymes responsible for maintaining high levels of estrogens in breast tumor cells, is associated with the membrane of the endoplasmic reticulum (ER). The structure of ES, purified from the microsomal fraction of human placentas, has been determined at 2.60-A resolution by x-ray crystallography. This structure shows a domain consisting of two antiparallel alpha-helices that protrude from the roughly spherical molecule, thereby giving the molecule a "mushroom-like" shape. These highly hydrophobic helices, each about 40 A long, are capable of traversing the membrane, thus presumably anchoring the functional domain on the membrane surface facing the ER lumen. The location of the transmembrane domain is such that the opening to the active site, buried deep in a cavity of the "gill" of the "mushroom," rests near the membrane surface, thereby suggesting a role of the lipid bilayer in catalysis. This simple architecture could be a prototype utilized by the ER membrane in dictating the form and the function of ER-resident enzymes.

Does deficiency of arylsulfatase B have a role in cystic fibrosis?

Cystic fibrosis (CF) is associated with mutation and abnormal function of the cystic fibrosis transmembrane conductance regulator (CFTR) that affects cellular chloride transport. Clinically, CF of the lung is associated with excessive accumulation of secretions, including the sulfated glycosaminoglycans, chondroitin sulfate and dermatan sulfate (DS), both of which contain sulfated N-acetylgalactosamine residues. The sulfatase enzymes, which are a highly conserved group of enzymes with high specificity for designated sulfate groups, include arylsulfatase B, a lysosomal enzyme. Arylsulfatase B, also known as N-acetyl galactosamine 4-sulfatase, can degrade DS and chondroitin-4 sulfate. Previously reported data demonstrated diminished activity of arylsulfatase B in lymphoid cell lines of patients with CF compared to normal control subjects. Frequent infections with Pseudomonas, a sulfatase-producing organism, occur in patients with CF, whereas infections with Mycobacterium tuberculosis, which lacks sulfatase activity, are infrequent. Additional investigation to determine if diminished function of arylsulfatase B is a consistent finding in cells of patients with CF may be informative, and may help to correlate the molecular, biochemical, and clinical characteristics of CF.

The multiple sulfatase deficiency gene encodes an essential and limiting factor for the activity of sulfatases

In multiple sulfatase deficiency (MSD), a human inherited disorder, the activities of all sulfatases are impaired due to a defect in posttranslational modification. Here we report the identification, by functional complementation using microcell-mediated chromosome transfer, of a gene that is mutated in MSD and is able to rescue the enzymatic deficiency in patients' cell lines. Functional conservation of this gene was observed among distantly related species, suggesting a critical biological role. Coexpression of SUMF1 with sulfatases results in a strikingly synergistic increase of enzymatic activity, indicating that SUMF1 is both an essential and a limiting factor for sulfatases. These data have profound implications on the feasibility of enzyme replacement therapy for eight distinct inborn errors of metabolism.

Insights into the catalytic mechanism of cofactor-independent phosphoglycerate mutase from X-ray crystallography, simulated dynamics and molecular modeling

Phosphoglycerate mutases catalyze the isomerization of 2 and 3-phosphoglycerates, and are essential for glucose metabolism in most organisms. Here, we further characterize the 2,3-bisphosphoglycerate-independent phosphoglycerate mutase (iPGM) from Bacillus stearothermophilus by determination of a high-resolution (1.4A) crystal structure of the wild-type enzyme and the crystal structure of its S62A mutant. The mutant structure surprisingly showed the replacement of one of the two catalytically essential manganese ions with a water molecule, offering an additional possible explanation for its lack of catalytic activity. Crystal structures invariably show substrate phosphoglycerate to be entirely buried in a deep cleft between the two iPGM domains. Flexibility analyses were therefore employed to reveal the likely route of substrate access to the catalytic site through an aperture created in the enzyme's surface during certain stages of the catalytic process. Several conserved residues lining this aperture may contribute to orientation of the substrate as it enters. Factors responsible for the retention of glycerate within the phosphoenzyme structure in the proposed mechanism are identified by molecular modeling of the glycerate complex of the phosphoenzyme. Taken together, these results allow for a better understanding of the mechanism of action of iPGMs. Many of the results are relevant to a series of evolutionarily related enzymes. These studies will facilitate the development of iPGM inhibitors which, due to the demonstrated importance of this enzyme in many bacteria, would be of great potential clinical significance.

The heparin/heparan sulfate 2-O-sulfatase from Flavobacterium heparinum. A structural and biochemical study of the enzyme active site and saccharide substrate specificity

In the previous paper (Myette, J. R., Shriver, Z., Claycamp, C., McLean, M. W., Venkataraman, G., and Sasisekharan, R. (2003) J. Biol. Chem. 278, 12157-12166), we described the molecular cloning, recombinant expression, and preliminary biochemical characterization of the heparin/heparan sulfate 2-O-sulfatase from Flavobacterium heparinum. In this paper, we extend our structure-function investigation of the 2-O-sulfatase. First, we have constructed a homology-based structural model of the enzyme active site, using as a framework the available crystallographic data for three highly related arylsulfatases. In this model, we have identified important structural parameters within the enzyme active site relevant to enzyme function, especially as they relate to its substrate specificity. By docking various disaccharide substrates, we identified potential structural determinants present within these substrates that would complement this unique active site architecture. These determinants included the position and number of sulfates present on the glucosamine, oligosaccharide chain length, the presence of a Delta4,5-unsaturated double bond, and the exolytic versus endolytic potential of the enzyme. The predictions made from our model provided a structural basis of substrate specificity originally interpreted from the biochemical and kinetic data. Our modeling approach was further complemented experimentally using peptide mapping in tandem with mass spectrometry and site-directed mutagenesis to physically demonstrate the presence of a covalently modified cysteine (formylglycine) within the active site. This combinatorial approach of structure modeling and biochemical studies provides insight into the molecular basis of enzyme function.

The heparin/heparan sulfate 2-O-sulfatase from Flavobacterium heparinum. Molecular cloning, recombinant expression, and biochemical characterization

Heparan sulfate glycosaminoglycans are structurally complex polysaccharides critically engaged in a wide range of cell and tissue functions. Any structure-based approach to study their respective biological functions is facilitated by the use of select heparan sulfate glycosaminoglycan-degrading enzymes with unique substrate specificities. We recently reported of one such enzyme, the Delta4,5-glycuronidase cloned from Flavobacterium heparinum and recombinantly expressed in Escherichia coli (Myette, J. R., Shriver, Z., Kiziltepe, T., McLean, M. W., Venkataraman, G., and Sasisekharan, R. (2002) Biochemistry 41, 7424-7434). In this study, we likewise report the molecular cloning of the 2-O-sulfatase from the same bacterium and its recombinant expression as a soluble, highly active enzyme. At the protein level, the flavobacterial 2-O-sulfatase possesses considerable sequence homology to other members of a large sulfatase family, especially within its amino terminus, where the highly conserved sulfatase domain is located. Within this domain, we have identified by sequence homology the critical active site cysteine predicted to be chemically modified as a formylglycine in vivo. We also present a characterization of the biochemical properties of the enzyme as it relates to optimal in vitro reaction conditions and a kinetic description of its substrate specificity. In particular, we demonstrate that in addition to the fact that the enzyme exclusively hydrolyzes the sulfate at the 2-O-position of the uronic acid, it also exhibits a kinetic preference for highly sulfated glucosamines within each disaccharide unit, especially those possessing a 6-O-sulfate. The sulfatase also displays a clear kinetic preference for disaccharides with beta1-->4 linkages but is able, nevertheless, to hydrolyze unsaturated, 2-O-sulfated chondroitin disaccharides. Finally, we describe the substrate-product relationship of the 2-O-sulfatase to the Delta4,5-glycuronidase and the analytical value of using both of these enzymes in tandem for elucidating heparin/heparan sulfate composition.

Porcine N-acetylgalactosamine 6-sulfatase (GALNS) cDNA sequence and expression in developing teeth

Mucopolysaccharidosis type IVA (Morquio A syndrome, MPS IVA) is a rare, autosomal recessive disorder with a prevalence of 1 in 170,000 live births. It is caused by a deficiency of N-acetylgalactosamine 6-sulfatase (GALNS), a lysosomal hydrolase encoded by a gene on human chromosome 16q24.3. Mucopolysaccharidosis type IVA is the only known MPS that is associated with structural defects in dental enamel. GALNS cleaves the sulfate group from N-acetylgalactosamine 6-sulfate and galactose 6-sulfate, which are specifically found in keratan sulfate and chondroitin 6-sulfate. A pathologic absence of GALNS activity results in the accumulation of these glycosaminoaglycans in the urine and in the lysosomes of tissues that turn them over. There is currently no animal model for MPS IVA. To learn more about how a GALNS deficit could lead to enamel defects, we have cloned and characterized a full-length pig GALNS cDNA. GALNS mRNA was localized in developing teeth by in situ hybridization, Northern blot, and reverse-transcription polymerase chain reaction analyses, while GALNS substrates were localized using immunohistochemistry. We report that secretory ameloblasts were positive for GALNS mRNA, as well as for keratan sulfate and chondroitin 6-sulfate. We conclude that enamel defects associated with the loss of GALNS activity in persons with MPS IVA are likely to result from the pathological accumulation of keratan sulfate and chondroitin 6-sulfate in the lysosomes of secretory stage ameloblasts.