P-nitrocatechol Sulfate Research Articles

Cloning and Characterization of a Novel N-Acetyl-D-galactosamine-4-O-sulfate Sulfatase, SulA1, from a Marine Arthrobacter Strain.

Sulfation is gaining increased interest due to the role of sulfate in the bioactivity of many polysaccharides of marine origin. Hence, sulfatases, enzymes that control the degree of sulfation, are being more extensively researched. In this work, a novel sulfatase (SulA1) encoded by the gene sulA1 was characterized. The sulA1-gene is located upstream of a chondroitin lyase encoding gene in the genome of the marine Arthrobacter strain (MAT3885). The sulfatase was produced in Escherichia coli. Based on the primary sequence, the enzyme is classified under sulfatase family 1 and the two catalytic residues typical of the sulfatase 1 family-Cys57 (post-translationally modified to formyl glycine for function) and His190-were conserved. The enzyme showed increased activity, but not improved stability, in the presence of Ca2+, and conserved residues for Ca2+ binding were identified (Asp17, Asp18, Asp277, and Asn278) in a structural model of the enzyme. The temperature and pH activity profiles (screened using p-nitrocatechol sulfate) were narrow, with an activity optimum at 40-50 °C and a pH optimum at pH 5.5. The Tm was significantly higher (67 °C) than the activity optimum. Desulfation activity was not detected on polymeric substrates, but was found on GalNAc4S, which is a sulfated monomer in the repeated disaccharide unit (GlcA-GalNAc4S) of, e.g., chondroitin sulfate A. The position of the sulA1 gene upstream of a chondroitin lyase gene and combined with the activity on GalNAc4S suggests that there is an involvement of the enzyme in the chondroitin-degrading cascade reaction, which specifically removes sulfate from monomeric GalNAc4S from chondroitin sulfate degradation products.

Genetic analysis of a family with metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) is a rare autosomal recessive lysosomal storage disease caused by a deficiency of the enzyme arylsulfatase A (ARSA), which is encoded by the ARSA gene. Mutations discovered in the ARSA gene continuously improve our knowledge and understanding of this rare disease. We identified a Chinese family with 15 members. Two of them were diagnosed as MLD. We used Sanger sequencing to analyze eight exons of the ARSA gene and measured the ARSA activity in leukocyte or amniotic cells with p-nitrocatechol sulfate as the substrate. The potential pathological functions of these variants were predicted through SIFT, Polyphen2, and Mutation Taster. Two family members with a diagnosis of MLD were a two-year-old boy and a fetus. Both had a complex heterozygous mutation: c.413C > T (p.Pro138Leu) in exon 2 and c.1344dupC (p.G449fs) in exon 8. This complex heterozygous mutation is the first case of concurrent missense and code shift mutations reported in MLD in China. In these two family members, ARSA activity (20 nmol/17 h/mg protein and 9.8 nmol/17 h/mg protein) is only 10% compared to the normal population.

The eukaryotic enzyme Bds1 is an alkyl but not an aryl sulfohydrolase

The eukaryotic enzyme Bds1 in Saccharomyces cerevisiae is a metallo-β-lactamase-related enzyme evolutionarily originating from bacterial horizontal gene transfer that serves an unknown biological role. Previously, Bds1 was reported to be an alkyl and aryl sulfatase. However, we demonstrate here that Bds1 acts on primary alkyl sulfates (of 6–12 carbon atoms) but not the aryl sulfates p-nitrophenyl sulfate and p-nitrocatechol sulfate. The apparent catalytic rate constant for hydrolysis of the substrate 1-hexyl sulfate by Bds1 is over 100 times lower than that of the reaction catalyzed by its bacterial homolog SdsA1. We show that Bds1 shares a catalytic mechanism with SdsA1 in which the carbon atom of the sulfate ester is the subject of nucleophilic attack, rather than the sulfur atom, resulting in C–O bond lysis. In contrast to SdsA1 and another bacterial homolog with selectivity for secondary alkyl sulfates named Pisa1, Bds1 does not show any substantial activity towards secondary alkyl sulfates. Neither Bds1 nor SdsA1 have any significant activity towards a branched primary alkyl sulfate, primary and secondary steroid sulfates, or phosphate diesters. Therefore, the enzymes homologous to SdsA1 that have been identified and characterized thus far vary in their selectivity towards primary and secondary alkyl sulfates but do not exhibit aryl sulfatase activity.

Conformational basis for substrate recruitment in protein tyrosine phosphatase 10D.

The coordinated activity of protein tyrosine phosphatases (PTPs) is crucial for the initiation, modulation, and termination of diverse cellular processes. The catalytic activity of this protein depends on a nucleophilic cysteine at the active site that mediates the hydrolysis of the incoming phosphotyrosine substrate. While the role of conserved residues in the catalytic mechanism of PTPs has been extensively examined, the diversity in the mechanisms of substrate recognition and modulation of catalytic activity suggests that other, less conserved sequence and structural features could contribute to this process. Here we describe the crystal structures of Drosophila melanogaster PTP10D in the apo form as well as in a complex with a substrate peptide and an inhibitor. These studies reveal the role of aromatic ring stacking interactions at the boundary of the active site of PTPs in mediating substrate recruitment. We note that phenylalanine 76, of the so-called KNRY loop, is crucial for orienting the phosphotyrosine residue toward the nucleophilic cysteine. Mutation of phenylalanine 76 to leucine results in a 60-fold decrease in the catalytic efficiency of the enzyme. Fluorescence measurements with a competitive inhibitor, p-nitrocatechol sulfate, suggest that Phe76 also influences the formation of the enzyme-substrate intermediate. The structural and biochemical data for PTP10D thus highlight the role of relatively less conserved residues in PTP domains in both substrate recruitment and modulation of reaction kinetics.

Rat intestinal microbiota digest desulfosinigrin to form allyl cyanide and 1-cyano-2,3-epithiopropane

The ability of rat intestinal microbiota to digest sinigrin and desulfosinigrin was studied using high performance liquid chromatography (HPLC) and gas chromatography–mass spectrometry (GC–MS). When sinigrin was incubated with rat intestinal microbiota, up to 64% of the initial amount of sinigrin was degraded during 12 h, yielding allyl isothiocyanate (AITC) as the major product along with a minor amount of allyl cyanide (ACN) and a trace amount of 1-cyano-2,3-epithiopropane (CETP), although the amount of ACN exceeded that of AITC after 12 h of incubation. In contrast, when desulfosinigrin was incubated with rat intestinal microbiota for 6 h, desulfosinigrin was digested up to 69% to form ACN and CETP as the major products instead of AITC. Whether the epithiospecifier protein (ESP) is involved in CETP formation in the rat intestinal microbiota-mediated degradation of desulfosinigrin remains to be established. However, only a trace amount of desulfosinigrin was detected during incubation of sinigrin with intestinal microbiota, although the intestinal microbiota had distinct sulfatase activity when p-nitrocatechol sulfate was used as the substrate. This observation suggested that the sulfatase of the rat intestinal microbiota has a very poor specificity toward sinigrin, which may be one reason for the formation of trace amounts of CETP during the intestinal microbiota-mediated digestion of sinigrin.

Inhibition of a Protein Tyrosine Phosphatase Using Mesoporous Oxides

The feasibility of utilizing mesoporous matrices of alumina and silica for the inhibition of enzymatic activity is presented here. These studies were performed on a protein tyrosine phosphatase by the name chick retinal tyrosine phosphotase-2 (CRYP-2), a protein that is identical in sequence to the human glomerular epithelial protein-1 and involved in hepatic carcinoma. The inhibition of CRYP-2 is of tremendous therapeutic importance. Inhibition of catalytic activity was examined using the sustained delivery of p-nitrocatechol sulfate (pNCS) from bare and amine functionalized mesoporous silica (MCM-48) and mesoporous alumina (Al(2)O(3)). Among the various mesoporous matrices employed, amine functionalized MCM-48 exhibited the best release of pNCS and also inhibition of CRYP-2. The maximum speed of reaction v(max) (=160 +/- 10 micromol/mnt/mg) and inhibition constant K(i) (=85.0 +/- 5.0 micromol) estimated using a competitive inhibition model were found to be very similar to inhibition activities of protein tyrosine phosphatases using other methods.

Interaction of arylsulfatase-A (ASA) with its natural sulfoglycolipid substrates: a computational and site-directed mutagenesis study

Arylsulfatase A (ASA) hydrolyzes sulfate esters with a pH optimum of 5. Interactions between p-nitrocatechol sulfate (NCS, artificial substrate) and active site residues of ASA are revealed from their co-crystal structure. Since equivalent ASA interactions with its natural substrates, sulfogalactosylceramide (SGC) and sulfogalactosylglycerolipid (SGG), are not known, we computationally docked SGC/SGG to the ASA crystal structure. Our dockings suggested that Cys69 was the active site residue, and Lys302 & Lys123 as residues anchoring the sulfate group of SGC/SGG to the active site, as observed for NCS. We further confirmed these results using 2 recombinant ASA mutants: C69A and CKK (Cys69, Lys302 and Lys123-all mutated to Ala). Both ASA mutants failed to desulfate SGC/SGG, and CKK showed minimal binding to [(14)C]SGC, although C69A still had affinity for this sulfoglycolipid. However, our dockings suggested additional intermolecular hydrogen bonding and hydrophobic interactions between ASA and SGC/SGG, thus contributing to the specificity of SGC/SGG as natural substrates.

Presence of Arylsulfatase A and Sulfogalactosylglycerolipid in Mouse Ovaries: Localization to the Corpus Luteum

Arylsulfatase A (AS-A) is a lysosomal enzyme, which catalyzes the desulfation of certain sulfogalactolipids, including sulfogalactosylglycerolipid (SGG), a molecule implicated in cell adhesion. In this report, immunocytochemistry revealed the selective presence of AS-A in the corpus luteum of mouse ovaries. Immunoblotting indicated that mouse corpus luteum AS-A had a molecular mass of 66 kDa, similar to AS-A of other tissues. Corpus luteum AS-A was active, capable of desulfating the artificial substrate, p-nitrocatechol sulfate, at the optimum pH of five. To understand further the role of AS-A in female reproduction, levels of AS-A were determined during corpus luteum development in pseudopregnant mice and during luteolysis after cessation of pseudopregnancy. Immunocytochemistry, immunoblotting and desulfation activity showed that AS-A expression was evident at the onset of pseudopregnancy in the newly formed corpora lutea, and its level increased steadily during gland development. The increase in the expression and activity of AS-A continued throughout luteolysis after the decrease in serum progesterone levels. We also observed the selective presence of SGG on the luteal cell surface in developed corpora lutea, as shown by immunofluorescence of mouse ovary sections as well as high-performance thin-layer chromatography of lipids isolated from mouse and pig corpora lutea. The identity of the "SGG" band on the thin layer silica plate was further validated by electrospray ionization mass spectrometry. Significantly, SGG disappeared in regressing corpora lutea. Therefore, lysosomal AS-A may be involved in cell-surface remodeling during luteolysis by desulfating SGG after its endocytosis and targeting to the lysosome.

Arylsulfatase G, a Novel Lysosomal Sulfatase

The sulfatases constitute a conserved family of enzymes that specifically hydrolyze sulfate esters in a wide variety of substrates such as glycosaminoglycans, steroid sulfates, or sulfolipids. By modifying the sulfation state of their substrates, sulfatases play a key role in the control of physiological processes, including cellular degradation, cell signaling, and hormone regulation. The loss of sulfatase activity has been linked with various severe pathophysiological conditions such as lysosomal storage disorders, developmental abnormalities, or cancer. A novel member of this family, arylsulfatase G (ASG), was initially described as an enzyme lacking in vitro arylsulfatase activity and localizing to the endoplasmic reticulum. Contrary to these results, we demonstrate here that ASG does indeed have arylsulfatase activity toward different pseudosubstrates like p-nitrocatechol sulfate and 4-methylumbelliferyl sulfate. The activity of ASG depends on the Cys-84 residue that is predicted to be post-translationally converted to the critical active site C(alpha)-formylglycine. Phosphate acts as a strong, competitive ASG inhibitor. ASG is active as an unprocessed 63-kDa monomer and shows an acidic pH optimum as typically seen for lysosomal sulfatases. In transfected cells, ASG accumulates within lysosomes as indicated by indirect immunofluorescence microscopy. Furthermore, ASG is a glycoprotein that binds specifically to mannose 6-phosphate receptors, corroborating its lysosomal localization. ARSG mRNA expression was found to be tissue-specific with highest expression in liver, kidney, and pancreas, suggesting a metabolic role of ASG that might be associated with a so far non-classified lysosomal storage disorder.

A Mining Minima Approach to Exploring the Docking Pathways of p-Nitrocatechol Sulfate to YopH

Using the docking of p-nitrocatechol sulfate to Yersinia protein tyrosine phosphatase YopH as an example, we showed that an approach based on mining minima followed by cluster and similarity analysis could generate useful insights into docking pathways. Our simulation treated both the ligand and the protein as flexible molecules so that the coupling between their motion could be properly accounted for. Our simulation identified three docking poses; the one with the lowest energy agreed well with experimental structure. The model also predicted the side-chain conformations of the amino acids lying in the binding pocket correctly with the exception of three residues that appeared to be stabilized by two structural water molecules in the crystal structure. The implicit solvent model employed in the simulation could not capture such effects well. We also found four major pathways leading to these docking poses after the ligand entered the mouth of the binding pocket. In addition, the sulfate group of p-nitrocatechol sulfate was found to be important both in binding the ligand to the pocket and in guiding the ligand to dock into the pocket. The coupling of the motion between the protein and the ligand also played an important role in facilitating ligand loading and unloading.

Loop Dynamics and Ligand Binding Kinetics in the Reaction Catalyzed by the Yersinia Protein Tyrosine Phosphatase

The Yersinia protein tyrosine phosphatase (YopH) contains a loop of ten amino acids (the WPD loop) that covers the entrance of the active site of the enzyme during substrate binding. In this work the substrate mimicking competitive inhibitor p-nitrocatechol sulfate (PNC) is used as a probe of the active site. The dynamics of the WPD loop was determined by subjecting an equilibrated system containing YopH, PNC, and YopH bound to PNC to a laser induced temperature jump, and subsequently following the change in equilibrium due to the perturbation. Using this methodology the dynamics associated with substrate binding in YopH have been determined. These results indicate that substrate binding is coupled to the WPD loop motion, and WPD loop dynamics occur in the sub-millisecond time scale. The significance of these dynamic results is interpreted in terms of the catalytic cycle of the enzyme.

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.

429. AAV5-Mediated Delivery of Human Aryl Sulfatase A (hARSA) Prevents Sufatide Storage and Neuropathological Phenotype in Metachromatic Leukodystrophy (MLD) Mice

Metachromatic leukodystrophy (MLD) is an inborn lysosomal storage disease caused by arylsulfatase A (ARSA) enzyme deficiency. Lack of ARSA results in the storage of galactosyl-3-sulfate ceramide (sulfatide) in neurons and glial cells that leads to progressive demyelination and neuronal damage in the CNS. The most severe form of MLD is the late infantile form that results in rapid loss of motor and cognitive functions and death within 2-5 years. No efficient therapy is available in infantile form of MLD and allogeneic hematopoietic cell transplantation has limited effects in the juvenile forms of MLD. MLD mice exhibit phenotypic abnormalities reminiscent of the human disease that include sulfatide storage in neurons and glial cells and neuromotor impairment. AAV5 vector encoding human ARSA was injected in the internal capsules and cerebellum of 3 month-old MLD mice (3 x109 vp /injection; n= 14) at the time they are beginning to develop CNS disease. Treated mice and mock-treated mice (AAV5-LacZ) were sacrificed at 6 and 18 months of age. Functional recombinant hARSA was detected in almost all areas of the forebrain, cerebellum and brainstem of AAV5-hARSA treated mice, using an ELISA assay that recognizes specifically the hARSA, immunohistochemistry and measurement of hARSA activity with the artificial substrate p-nitrocatechol sulfate. As expected, hARSA was mostly expressed in neurons, but also in a significant percentage of astrocytes (up to 14% arround the injection site) and in microglial cells. The widespread diffusion of hARSA resulted from both vector and enzyme diffusion within the CNS. Quantitative PCR in AAV5-ARSA vector showed that vector genomes were concentrated at the injection sites but spreads over a distance from injection sites. ARSA expression using ELISA test was proportional to the number of vector genomes but extended far beyond PCR-positive brain regions. The increase of ARSA positive neurons and astrocytes from 6 to 18 months of age confirmed that a significant amount of AAV5-encoded ARSA was secreted by transduced cells and captured by neurons and astrocytes. ARSA delivery prevented sulfatide deposits and reversed the galactosyl ceramide/sulfatide abnormal ratio that reflects sulfatide storage and loss of oligodendrocytes. Eighteen-month old treated mice showed a nearly absence of neuropathological abnormalities (Purkinje cell loss, astrogliosis, microglial activation) and normal motor behavior (at the rotarod test). These results indicate that ARSA delivery from intracerebral sources has the capacity to alleviate most disease manifestation in the MLD model.

Characterization of arylsulfatase activity in brine shrimp, Artemia salina

Arylsulfatase from Artemia salina exists in at least two forms (AS I and AS II). The paper presents characterization of the AS II form of the arylsulfatase. The enzyme was able to hydrolyze p-nitrocatechol sulfate (pNCS) as well as ascorbate sulfate. It exhibited maximum activity at temperature of 50 °C and was stable for 2 h at 4–10 °C. Optimum pH shifted from 6.2 at 4 mM pNCS (substrate) to 4.8 at 20 mM pNCS. The enzyme displayed linear kinetics. AS II arylsulfatase exists in two molecular forms (349 and 460 kDa) composed of identical subunits with molecular mass of 53 kDa. Sulfite and phosphate ions were the most potent inhibitors of the enzyme. Cyanide proved to be a weak inhibitor. Sulfate and low concentrations of silver ions had no effect on the enzyme activity. Based on the above results, modifications in the assay for determination of enzyme activity are proposed.

Crystal Structure of the Yersinia Protein-tyrosine Phosphatase YopH Complexed with a Specific Small Molecule Inhibitor

The pathogenic bacteria Yersinia are causative agents in human diseases ranging from gastrointestinal syndromes to bubonic plague. There is increasing risk of misuse of infectious agents, such as Yersinia pestis, as weapons of terror as well as instruments of warfare for mass destruction. Because the phosphatase activity of the Yersinia protein tyrosine phosphatase, YopH, is essential for virulence in the Yersinia pathogen, potent and selective YopH inhibitors are expected to serve as novel anti-plague agents. We have identified a specific YopH small molecule inhibitor, p-nitrocatechol sulfate (pNCS), which exhibits a Ki value of 25 microM for YopH and displays a 13-60-fold selectivity in favor of YopH against a panel of mammalian PTPs. To facilitate the understanding of the underlying molecular basis for tight binding and specificity, we have determined the crystal structure of YopH in complex with pNCS at a 2.0-A resolution. The structural data are corroborated by results from kinetic analyses of the interactions of YopH and its site-directed mutants with pNCS. The results show that while the interactions of the sulfuryl moiety and the phenyl ring with the YopH active site contribute to pNCS binding affinity, additional interactions of the hydroxyl and nitro groups in pNCS with Asp-356, Gln-357, Arg-404, and Gln-446 are responsible for the increased potency and selectivity. In particular, we note that residues Arg-404, Glu-290, Asp-356, and a bound water (WAT185) participate in a unique H-bonding network with the hydroxyl group ortho to the sulfuryl moiety, which may be exploited to design more potent and specific YopH inhibitors.

Molecular and biochemical characterisation of a novel sulphatase gene: Arylsulfatase G (ARSG).

Molecular analysis has provided important insights into the biochemistry and genetics of the sulphatase family of enzymes. Through bioinformatic searches of the EST database, we have identified a novel gene consisting of 11 exons and encoding a 525 aa protein that shares a high degree of sequence similarity with all sulphatases and in particular with arylsulphatases, hence the tentative name Arylsulfatase G (ARSG). The highest homology is shared with Arylsulfatase A, a lysosomal sulphatase which is mutated in metachromatic leukodistrophy, particularly in the amino-terminal region. The 10 amino acids that form the catalytic site are strongly conserved. The murine homologue of Arylsulfatase G gene product shows 87% identity with the human protein. To test the function of this novel gene we transfected the full-length cDNA in Cos7 cells, and detected an Arylsulfatase G precursor protein of 62 kDa. After glycosylation the precursor is maturated in a 70 kDa form, which localises to the endoplasmic reticulum. Northern blot analysis of Arylsulfatase G revealed a ubiquitous expression pattern. We tested the sulphatase activity towards two different artificial substrates 4-methylumbelliferyl (4-MU) sulphate and p-nitrocatechol sulphate, but no arylsulphatase activity was detectable. Further studies are needed to characterise the function of Arylsulfatase G, possibly revealing a novel metabolic pathway.

Croatian Population Data for Arylsulfatase A Pseudodeficiency-Associated Mutations in Healthy Subjects, and in Patients with Alzheimer-Type Dementia and Down Syndrome

Background Arylsulfatase A (ASA) is a lysosomal enzyme involved in catabolism of cerebroside sulfate, whose deficiency causes metachromatic leukodystrophy, a rare autosomal recessive disorder characterized by storage of cerebroside sulfate, mainly in the nervous system. Low ASA activities have also been reported in healthy individuals and several neuropsychiatric disorders due to the condition termed ASA pseudodeficiency. The aim of this study was to establish frequency of two mutations associated with ASA pseudodeficiency in healthy individuals in the Croatian population as well as in persons with Alzheimer-type dementia and Down syndrome. Methods Presence of N350S and 1524+95 A→G pseudodeficiency mutations was detected in genomic DNA extracted from leukocytes of healthy subjects ( n = 125) and of patients with Alzheimer-type dementia ( n = 18) and Down syndrome ( n = 21). Arylsulfatase A activity was measured in leukocyte homogenates by spectrophotometry (λ = 515 nm) using p-nitrocatechol sulfate as chromogenic substrate. Results Frequency of N350S mutation and mutation 1524+95 A→G was estimated at 6.8 and 2.8% for healthy controls, 11 and 5.5% for Alzheimer-type dementia, and 12 and 9.5% for Down syndrome, respectively. Arylsulfatase A activity was slightly but not significantly decreased in leukocytes derived from subjects with dementia and Down syndrome in comparison with age-matched control samples. Conclusions Frequency of two mutations associated with ASA pseudodeficiency in the Croatian population is slightly below the range reported for other populations. Additionally, despite the proposed role of arylsulfatase A pseudodeficiency as one of the predisposing factors for neuropsychiatric disorders, our preliminary results did not show significantly higher frequencies of either mutation in Alzheimer-type dementia or Down syndrome.

Low Arylsulphatase A Activity in the Development of Psychiatric Disorders

Previous studies have suggested that arylsulphatase A (ASA) deficiency may be present in psychiatric patients. A number of patients with low ASA activity and various neuropsychiatric symptoms have been observed. Metachromatic leucodystrophy (MLD) is a disease caused by deficiency of the enzyme ASA. Clinically, adult MLD may present as a schizophrenia-like psychosis, deterioration of cognitive functions, personality changes, depression and dementia. However, there are individuals with low ASA activity without clinical symptoms of MLD. This state is described as ASA pseudodeficiency. It remains controversial whether low ASA activity predisposes to or influences the development of psychiatric symptoms. Relatively little attention has been paid to the role of neurodegenerative processes in the pathophysiology of psychiatric disorders. The hypothesis underlying this work is that there is a subclass of mentally ill patients whose psychiatric problems are at least partly caused by an abnormal ASA. The purpose of this particular study was to determine whether an abnormal ASA could be detected in schizoprenic, major depressed and demented patients and control subjects. There were 66 schizophrenic, 59 major depressed and 61 demented patients. The control group consisted of 102 healthy volunteers. Leucocyte ASA activity was determined from blood samples, using p-nitrocatechol sulphate as substrate. Our results show that low ASA activity is more frequently found in psychiatric patients than in control subjects. Our findings indicate that clinical types of major depression and schizophrenia could be connected with low ASA activity. The presence of a decreased ASA activity points to the conclusion that an enzyme deficit entails vulnerability to psychiatric disorders.

Crystal Structure of an Enzyme-Substrate Complex Provides Insight into the Interaction between Human Arylsulfatase A and its Substrates During Catalysis

Arylsulfatase A (ASA) belongs to the sulfatase family whose members carry a C α-formylglycine that is post-translationally generated by oxidation of a conserved cysteine or serine residue. The crystal structures of two arylsulfatases, ASA and ASB, and kinetic studies on ASA mutants led to different proposals for the catalytic mechanism in the hydrolysis of sulfate esters. The structures of two ASA mutants that lack the functional C α-formylglycine residue 69, in complex with a synthetic substrate, have been determined in order to unravel the reaction mechanism. The crystal structure of the inactive mutant C69A-ASA in complex with p-nitrocatechol sulfate (pNCS) mimics a reaction intermediate during sulfate ester hydrolysis by the active enzyme, without the covalent bond to the key side-chain FGly69. The structure shows that the side-chains of lysine 123, lysine 302, serine 150, histidine 229, the main-chain of the key residue 69 and the divalent cation in the active center are involved in sulfate binding. It is proposed that histidine 229 protonates the leaving alcoholate after hydrolysis. C69S-ASA is able to bind covalently to the substrate and hydrolyze it, but is unable to release the resulting sulfate. Nevertheless, the resulting sulfation is low. The structure of C69S-ASA shows the serine side-chain in a single conformation, turned away from the position a substrate occupies in the complex. This suggests that the double conformation observed in the structure of wild-type ASA is more likely to correspond to a formylglycine hydrate than to a twofold disordered aldehyde oxo group, and accounts for the relative inertness of the C69S-ASA mutant. In the C69S-ASA-pNCS complex, the substrate occupies the same position as in the C69A-ASA-pNCS complex, which corresponds to the non-covalently bonded substrate. Based on the structural data, a detailed mechanism for sulfate ester cleavage is proposed, involving an aldehyde hydrate as the functional group.

The potassium salt of p-nitrocatechol sulfate.

The structure of p-nitrocatechol sulfate dipotassium salt dihydrate (dipotassium 2-oxido-5-nitrophenyl sulfate dihydrate), K 2 (C 6 H 3 NO 7 S).H 2 O, is reported. An accurate structural determination was needed to derive reliable restraints for use in macromolecular refinement at medium resolution of a protein-substrate complex