Sulfated glycan recognition by carbohydrate sulfatases of the human gut microbiota

Sulfated glycans are ubiquitous nutrient sources for microbial communities that have coevolved with eukaryotic hosts. Bacteria metabolize sulfated glycans by deploying carbohydrate sulfatases that remove sulfate esters. Despite the biological importance of sulfatases, the mechanisms underlying their ability to recognize their glycan substrate remain poorly understood. Here, we use structural biology to determine how sulfatases from the human gut microbiota recognize sulfated glycans. We reveal seven new carbohydrate sulfatase structures spanning four S1 sulfatase subfamilies. Structures of S1_16 and S1_46 represent novel structures of these subfamilies. Structures of S1_11 and S1_15 demonstrate how non-conserved regions of the protein drive specificity toward related but distinct glycan targets. Collectively, these data reveal that carbohydrate sulfatases are highly selective for the glycan component of their substrate. These data provide new approaches for probing sulfated glycan metabolism while revealing the roles carbohydrate sulfatases play in host glycan catabolism.

Purification, Characterization, and Structural Studies of a Sulfatase from Pedobacter yulinensis

Sulfatases are ubiquitous enzymes that hydrolyze sulfate from sulfated organic substrates such as carbohydrates, steroids, and flavones. These enzymes can be exploited in the field of biotechnology to analyze sulfated metabolites in humans, such as steroids and drugs of abuse. Because genomic data far outstrip biochemical characterization, the analysis of sulfatases from published sequences can lead to the discovery of new and unique activities advantageous for biotechnological applications. We expressed and characterized a putative sulfatase (PyuS) from the bacterium Pedobacter yulinensis. PyuS contains the (C/S)XPXR sulfatase motif, where the Cys or Ser is post-translationally converted into a formylglycine residue (FGly). His-tagged PyuS was co-expressed in Escherichia coli with a formylglycine-generating enzyme (FGE) from Mycobacterium tuberculosis and purified. We obtained several crystal structures of PyuS, and the FGly modification was detected at the active site. The enzyme has sulfatase activity on aromatic sulfated substrates as well as phosphatase activity on some aromatic phosphates; however, PyuS did not have detectable activity on 17α-estradiol sulfate, cortisol 21-sulfate, or boldenone sulfate.

A single sulfatase is required to access colonic mucin by a gut bacterium

Humans have co-evolved with a dense community of microbial symbionts that inhabit the lower intestine. In the colon, secreted mucus creates a barrier that separates these microorganisms from the intestinal epithelium1. Some gut bacteria are able to utilize mucin glycoproteins, the main mucus component, as a nutrient source. However, it remains unclear which bacterial enzymes initiate degradation of the complex O-glycans found in mucins. In the distal colon, these glycans are heavily sulfated, but specific sulfatases that are active on colonic mucins have not been identified. Here we show that sulfatases are essential to the utilization of distal colonic mucin O-glycans by the human gut symbiont Bacteroides thetaiotaomicron. We characterized the activity of 12 different sulfatases produced by this species, showing that they are collectively active on all known sulfate linkages in O-glycans. Crystal structures of three enzymes provide mechanistic insight into the molecular basis of substrate specificity. Unexpectedly, we found that a single sulfatase is essential for utilization of sulfated O-glycans in vitro and also has a major role in vivo. Our results provide insight into the mechanisms of mucin degradation by a prominent group of gut bacteria, an important process for both normal microbial gut colonization2 and diseases such as inflammatory bowel disease3.

Discovery of a fucoidan endo-4O-sulfatase: Regioselective 4O-desulfation of fucoidans and its effect on anticancer activity in vitro

Fucoidans are a class of sulfated fucose-containing bioactive polysaccharides produced by brown algae. The biological effects exhibited by fucoidans are thought to be related to their sulfation. However, the lack of methods for sulfation control does not allow for a reliable conclusion about the influence of the position of certain sulfate groups on the observed biological effects. We identified the gene encoding the endo-acting fucoidan sulfatase swf5 in the marine bacterium Wenyingzhuangia fucanilytica CZ1127^T. This is the first report on the sequence of fucoidan endo-sulfatase. Sulfatase SWF5 belongs to the subfamily S1_22 of the family S1. SWF5 was shown to remove 4O-sulfation in fucoidans composed from the alternating α-(1→3)- and α-(1→4)-linked residues of sulfated L-fucose but not from fucoidans with the α-(1→3)-linked backbone. The endo-sulfatase was used to selectively prepare 4O-desulfated fucoidan derivatives. It was shown that the 4O-desulfated fucoidans inhibit colony formation of DLD-1 and MCF-7 cells less effectively than unmodified fucoidans. Presumably, 4O-sulfation makes a significant contribution to the anticancer activity of fucoidans.

The fallacy of enzymatic hydrolysis for the determination of bioactive curcumin in plasma samples as an indication of bioavailability: a comparative study

BACKGROUND

Numerous health benefits have been demonstrated for curcumin which is extracted from turmeric (Curcuma longa L). However, due to its poor absorption in the free form in the gastrointestinal tract and rapid biotransformation, various formulations have been developed to enhance its bioavailability. Previous studies indicate that the free form of curcumin is more bioactive than its conjugated counterparts in target tissues. Most curcumin pharmacokinetics studies in humans designed to assess its absorption and bioavailability have measured and reported total (free plus conjugated) curcumin, but not free, bioactive curcumin in the plasma because enzymatic hydrolysis was employed prior to its extraction and analysis. Therefore, the bioavailability of free curcumin cannot be determined.

METHODS

Eight human subjects (4 male, 4 female) consumed a single dose of 400 mg curcumin in an enhanced absorption formulation, and blood samples were collected over 6 h. Plasma was treated either with or without glucuronidase/sulfatase prior to extraction. Curcumin and its major metabolites were analyzed using HPLC-tandem mass spectrometry. In addition, the literature was searched for pharmacokinetic studies involving curcumin using PubMed and Google Scholar, and the reported bioavailability data were compared based on whether hydrolysis of plasma samples was used prior to sample analysis.

RESULTS

Hydrolysis of blood plasma samples prior to extraction and reporting the results as "curcumin" obscures the amount of free, bioactive curcumin and total curcuminoids as compared to non-hydrolyzed samples. As a consequence, the data and biological effects reported by most pharmacokinetic studies are not a clear indication of enhanced plasma levels of free bioactive curcumin due to product formulations, leading to a misrepresentation of the results of the studies and the products when enzymatic hydrolysis is employed.

CONCLUSIONS

When enzymatic hydrolysis is employed as is the case with most studies involving curcumin products, the amount of free bioactive curcumin is unknown and cannot be determined. Therefore, extreme caution is warranted in interpreting published analytical results from biological samples involving ingestion of curcumin-containing products.

TRIAL REGISTRATION

ClinicalTrails.gov, trial identifying number NCT04103788 , September 24, 2019. Retrospectively registered.

Transition-State Interactions in a Promiscuous Enzyme: Sulfate and Phosphate Monoester Hydrolysis by Pseudomonas aeruginosa Arylsulfatase

Pseudomonas aeruginosa arylsulfatase (PAS) hydrolyzes sulfate and, promiscuously, phosphate monoesters. Enzyme-catalyzed sulfate transfer is crucial to a wide variety of biological processes, but detailed studies of the mechanistic contributions to its catalysis are lacking. We present linear free energy relationships (LFERs) and kinetic isotope effects (KIEs) of PAS and analyses of active site mutants that suggest a key role for leaving group (LG) stabilization. In LFERs PASWT has a much less negative Brønsted coefficient (βleaving groupobs-Enz = -0.33) than the uncatalyzed reaction (βleaving groupobs = -1.81). This situation is diminished when cationic active site groups are exchanged for alanine. The considerable degree of bond breaking during the transition state (TS) is evidenced by an 18Obridge KIE of 1.0088. LFER and KIE data for several active site mutants point to leaving group stabilization by active site K375, in cooperation with H211. 15N KIEs and the increased sensitivity to leaving group ability of the sulfatase activity in neat D2O (Δβleaving groupH-D = +0.06) suggest that the mechanism for S-Obridge bond fission shifts, with decreasing leaving group ability, from charge compensation via Lewis acid interactions toward direct proton donation. 18Ononbridge KIEs indicate that the TS for PAS-catalyzed sulfate monoester hydrolysis has a significantly more associative character compared to the uncatalyzed reaction, while PAS-catalyzed phosphate monoester hydrolysis does not show this shift. This difference in enzyme-catalyzed TSs appears to be the major factor favoring specificity toward sulfate over phosphate esters by this promiscuous hydrolase, since other features are either too similar (uncatalyzed TS) or inherently favor phosphate (charge).

Directed Evolution of a Designer Enzyme Featuring an Unnatural Catalytic Amino Acid

The impressive rate accelerations that enzymes display in nature often result from boosting the inherent catalytic activities of side chains by their precise positioning inside a protein binding pocket. Such fine-tuning is also possible for catalytic unnatural amino acids. Specifically, the directed evolution of a recently described designer enzyme, which utilizes an aniline side chain to promote a model hydrazone formation reaction, is reported. Consecutive rounds of directed evolution identified several mutations in the promiscuous binding pocket, in which the unnatural amino acid is embedded in the starting catalyst. When combined, these mutations boost the turnover frequency (kcat ) of the designer enzyme by almost 100-fold. This results from strengthening the catalytic contribution of the unnatural amino acid, as the engineered designer enzymes outperform variants, in which the aniline side chain is replaced with a catalytically inactive tyrosine residue, by more than 200-fold.

Structure and expression of sulfatase and sulfatase modifying factor genes in the diamondback moth, Plutella xylostella

The diamondback moth, Plutella xylostella (L.), uses sulfatases (SULF) to counteract the glucosinolate-myrosinase defensive system that cruciferous plants have evolved to deter insect feeding. Sulfatase activity is regulated by post-translational modification of a cysteine residue by sulfatase modifying factor 1 (SUMF1). We identified 12 SULF genes (PxylSulfs) and two SUMF1 genes (PxylSumf1s) in the P. xylostella genome. Phylogenetic analysis of SULFs and SUMFs from P. xylostella, Bombyx mori, Manduca sexta, Heliconius melpomene, Danaus plexippus, Drosophila melanogaster, Tetranychus urticae and Homo sapiens showed that the SULFs were clustered into five groups, and the SUMFs could be divided into two groups. Profiling of the expression of PxylSulfs and PxylSumfs by RNA-seq and by quantitative real-time polymerase chain reaction showed that two glucosinolate sulfatase genes (GSS), PxylSulf2 and PxylSulf3, were primarily expressed in the midgut of 3rd- and 4th-instar larvae. Moreover, expression of sulfatases PxylSulf2, PxylSulf3 and PxylSulf4 were correlated with expression of the sulfatases modifying factor PxylSumf1a. The findings from this study provide new insights into the structure and expression of SUMF1 and PxylSulf genes that are considered to be key factors for the evolutionary success of P. xylostella as a specialist herbivore of cruciferous plants.

Structural and Mechanistic Analysis of the Choline Sulfatase from Sinorhizobium melliloti: A Class I Sulfatase Specific for an Alkyl Sulfate Ester

Hydrolysis of organic sulfate esters proceeds by two distinct mechanisms, water attacking at either sulfur (S-O bond cleavage) or carbon (C-O bond cleavage). In primary and secondary alkyl sulfates, attack at carbon is favored, whereas in aromatic sulfates and sulfated sugars, attack at sulfur is preferred. This mechanistic distinction is mirrored in the classification of enzymes that catalyze sulfate ester hydrolysis: arylsulfatases (ASs) catalyze S-O cleavage in sulfate sugars and arylsulfates, and alkyl sulfatases break the C-O bond of alkyl sulfates. Sinorhizobium meliloti choline sulfatase (SmCS) efficiently catalyzes the hydrolysis of alkyl sulfate choline-O-sulfate (kcat/KM=4.8×103s-1M-1) as well as arylsulfate 4-nitrophenyl sulfate (kcat/KM=12s-1M-1). Its 2.8-Å resolution X-ray structure shows a buried, largely hydrophobic active site in which a conserved glutamate (Glu386) plays a role in recognition of the quaternary ammonium group of the choline substrate. SmCS structurally resembles members of the alkaline phosphatase superfamily, being most closely related to dimeric ASs and tetrameric phosphonate monoester hydrolases. Although >70% of the amino acids between protomers align structurally (RMSDs 1.79-1.99Å), the oligomeric structures show distinctly different packing and protomer-protomer interfaces. The latter also play an important role in active site formation. Mutagenesis of the conserved active site residues typical for ASs, H218O-labeling studies and the observation of catalytically promiscuous behavior toward phosphoesters confirm the close relation to alkaline phosphatase superfamily members and suggest that SmCS is an AS that catalyzes S-O cleavage in alkyl sulfate esters with extreme catalytic proficiency.

How members of the human gut microbiota overcome the sulfation problem posed by glycosaminoglycans

The human microbiota, which plays an important role in health and disease, uses complex carbohydrates as a major source of nutrients. Utilization hierarchy indicates that the host glycosaminoglycans heparin (Hep) and heparan sulfate (HS) are high-priority carbohydrates for Bacteroides thetaiotaomicron, a prominent member of the human microbiota. The sulfation patterns of these glycosaminoglycans are highly variable, which presents a significant enzymatic challenge to the polysaccharide lyases and sulfatases that mediate degradation. It is possible that the bacterium recruits lyases with highly plastic specificities and expresses a repertoire of enzymes that target substructures of the glycosaminoglycans with variable sulfation or that the glycans are desulfated before cleavage by the lyases. To distinguish between these mechanisms, the components of the B. thetaiotaomicron Hep/HS degrading apparatus were analyzed. The data showed that the bacterium expressed a single-surface endo-acting lyase that cleaved HS, reflecting its higher molecular weight compared with Hep. Both Hep and HS oligosaccharides imported into the periplasm were degraded by a repertoire of lyases, with each enzyme displaying specificity for substructures within these glycosaminoglycans that display a different degree of sulfation. Furthermore, the crystal structures of a key surface glycan binding protein, which is able to bind both Hep and HS, and periplasmic sulfatases reveal the major specificity determinants for these proteins. The locus described here is highly conserved within the human gut Bacteroides, indicating that the model developed is of generic relevance to this important microbial community.

Expanding the genetic cause of multiple sulfatase deficiency: A novel SUMF1 variant in a patient displaying a severe late infantile form of the disease

Multiple sulfatase deficiency (MSD) is a rare inherited metabolic disease caused by defective cellular sulfatases. Activity of sulfatases depends on post-translational modification catalyzed by formylglycine-generating enzyme (FGE), encoded by the SUMF1 gene. SUMF1 pathologic variants cause MSD, a syndrome presenting with a complex phenotype. We describe the first Polish patient with MSD caused by a yet undescribed pathologic variant c.337G>A [p.Glu113Lys] (i.e. p.E113K) in heterozygous combination with the known deletion allele c.519+5_519+8del [p.Ala149_Ala173del]. The clinical picture of the patient initially suggested late infantile metachromatic leukodystrophy, with developmental delay followed by regression of visual, hearing and motor abilities as the most apparent clinical symptoms. Transient signs of ichthyosis and minor dysmorphic features guided the laboratory workup towards MSD. Since MSD is a rare disease and there is a variable clinical spectrum, we thoroughly describe the clinical outcome of our patient. The FGE-E113K variant, expressed in cell culture, correctly localized to the endoplasmic reticulum but was retained intracellularly in contrast to the wild type FGE. Analysis of FGE-mediated activation of steroid sulfatase in immortalized MSD cells revealed that FGE-E113K exhibited only approx. 15% of the activity of wild type FGE. Based on the crystal structure we predict that the exchange of glutamate-113 against lysine should induce a strong destabilization of the secondary structure, possibly affecting the folding for correct disulfide bridging between C235-C346 as well as distortion of the active site groove that could affect both the intracellular stability as well as the activity of FGE. Thus, the novel variant of the SUMF1 gene obviously results in functionally impaired FGE protein leading to a severe late infantile type of MSD.

Chondroitin sulfate/dermatan sulfate sulfatases from mammals and bacteria

Sulfatases that specifically catalyze the hydrolysis of the sulfate groups on chondroitin sulfate (CS)/dermatan sulfate (DS) poly- and oligosaccharides belong to the formylglycine-dependent family of sulfatases and have been widely found in various mammalian and bacterial organisms. However, only a few types of CS/DS sulfatase have been identified so far. Recently, several novel CS/DS sulfatases have been cloned and characterized. Advanced studies have provided significant insight into the biological function and mechanism of action of CS/DS sulfatases. Moreover, further studies will provide powerful tools for structural and functional studies of CS/DS as well as related applications. This article reviews the recent progress in CS/DS sulfatase research and is expected to initiate further research in this field.

Detection of Sulfatase Enzyme Activity with a CatalyCEST MRI Contrast Agent

A chemical exchange saturation transfer (CEST) MRI contrast agent has been developed that detects sulfatase enzyme activity. The agent produces a CEST signal at δ=5.0 ppm before enzyme activity, and a second CEST signal appears at δ=9.0 ppm after the enzyme cleaves a sulfate group from the agent. The comparison of the two signals improved detection of sulfatase activity.

Enzyme-Assisted Preparation of Furcellaran-Like κ-/β-Carrageenan

Carrageenans are sulfated galactans that are widely used in industrial applications for their thickening and gelling properties, which vary according to the amount and distribution of ester sulfate groups along the galactan backbone. To determine and direct the sulfation of κ-carrageenan moieties, we purified an endo-κ-carrageenan sulfatase (Q15XH1 accession in UniprotKB) from Pseudoalteromonas atlantica T6c extracts. Based on sequence analyses and exploration of the genomic environment of Q15XH1, we discovered and characterized a second endo-κ-carrageenan sulfatase (Q15XG7 accession in UniprotKB). Both enzymes convert κ-carrageenan into a hybrid, furcellaran-like κ-/β-carrageenan. We compared the protein sequences of these two new κ-carrageenan sulfatases and that of a previously reported ι-carrageenan sulfatase with other predicted sulfatases in the P. atlantica genome, revealing the existence of additional new carrageenan sulfatases.

Microbial alkyl- and aryl-sulfatases: mechanism, occurrence, screening and stereoselectivities

This review gives an overview on the occurrence of sulfatases in Prokaryota, Eukaryota and Archaea. The mechanism of enzymes acting with retention or inversion of configuration during sulfate ester hydrolysis is discussed taking two complementary examples. Methods for the discovery of novel alkyl sulfatases are described by way of sequence-based search and enzyme induction. A comprehensive list of organisms with their respective substrate scope regarding prim- and sec-alkyl sulfate esters allows to assess the capabilities and limitations of various biocatalysts employed as whole cell systems or as purified enzymes with respect to their activities and enantioselectivities. Methods for immobilization and selectivity enhancement by addition of metal ions or organic (co)solvents are summarised.

Mycobacterium tuberculosis Rv3406 is a type II alkyl sulfatase capable of sulfate scavenging

The genome of Mycobacterium tuberculosis (Mtb) encodes nine putative sulfatases, none of which have a known function or substrate. Here, we characterize Mtb’s single putative type II sulfatase, Rv3406, as a non-heme iron (II) and α-ketoglutarate-dependent dioxygenase that catalyzes the oxidation and subsequent cleavage of alkyl sulfate esters. Rv3406 was identified based on its homology to the alkyl sulfatase AtsK from Pseudomonas putida. Using an in vitro biochemical assay, we confirmed that Rv3406 is a sulfatase with a preference for alkyl sulfate substrates similar to those processed by AtsK. We determined the crystal structure of the apo Rv3406 sulfatase at 2.5 Å. The active site residues of Rv3406 and AtsK are essentially superimposable, suggesting that the two sulfatases share the same catalytic mechanism. Finally, we generated an Rv3406 mutant (Δrv3406) in Mtb to study the sulfatase’s role in sulfate scavenging. The Δrv3406 strain did not replicate in minimal media with 2-ethyl hexyl sulfate as the sole sulfur source, in contrast to wild type Mtb or the complemented strain. We conclude that Rv3406 is an iron and α-ketoglutarate-dependent sulfate ester dioxygenase that has unique substrate specificity that is likely distinct from other Mtb sulfatases.

Inter and intra plant variability of enzyme profiles including various phosphoesterases and sulfatase of six wastewater treatment plants

Biodegradation of organic wastewater constituents by activated sludge microorganisms is based on enzymatic processes. It is supposed that wastewater treatment plants (WWTP) differ in their enzymatic fingerprints. To determine such fingerprints, activated sludges from nine aerated tanks of six WWTPs were repeatedly sampled and analyzed for the activities of l-alanine aminopeptidase, esterase, α- and β-glucosidase, alkaline phosphatase, phosphodiesterase, phosphotriesterase, and sulfatase. In one WWTP the enzymatic activities and their variations within 1 week were assayed in various process stages. Mostly the enzymatic profiles were dominated by l-alanine aminopeptidase, followed by alkaline phosphatase. They differed in variable contributions of esterase, phosphodiesterase, α- and β-glucosidase. The sulfatase activity was generally low. For the first time phosphotriesterase activity was detected in various samples, but with limited analytical validity. Particle mass-related activities of individual enzymes varied between plants by factors 2-4 and up to 11, when related to suspension volumes.

Neutralizing the anticoagulant activity of ultra-low-molecular-weight heparins using N-acetylglucosamine 6-sulfatase

Heparin has been the most commonly used anticoagulant drug for nearly a century. The drug heparin is generally categorized into three forms according to its molecular weight: unfractionated (UF, average molecular weight 13 000), low molecular weight (average molecular weight 5000) and ultra-low-molecular-weight heparin (ULMWH, average molecular weight 2000). An overdose of heparin may lead to very dangerous bleeding in patients. Protamine sulfate may be administered as an antidote to reverse heparin's anticoagulant effect. However, there is no effective antidote for ULMWH. In the current study, we examine the use of human N-acetylglucosamine 6-sulfatase (NG6S), expressed in Chinese hamster ovary cells, as a reversal agent for ULMWH. NG6S removes a single 6-O-sulfo group at the non-reducing end of the ULMWH Arixtra(®) (fondaparinux), effectively removing its ability to bind to antithrombin and preventing its inhibition of coagulation factor Xa. These results pave the way to developing human NG6S as an antidote for neutralizing the anticoagulant activity of ULMWHs.

Simultaneous identification of tyrosine phosphorylation and sulfation sites utilizing tyrosine-specific bromination

Tyrosine phosphorylation and sulfation play many key roles in the cell. Isobaric phosphotyrosine and sulfotyrosine residues in peptides were determined by mass spectrometry using phosphatase or sulfatase to remove the phosphate or the sulfate group. Unique Br signature was introduced to the resulting tyrosine residues by incubation with 32% HBr at -20 °C for 20 min. MS/MS analysis of the brominated peptide enabled unambiguous determination of the phosphotyrosine and the sulfotyrosine sites. When phosphotyrosine and sulfotyrosine as well as free tyrosine were present in the same peptide, they could be determined simultaneously using either phosphatase or sulfatase following acetylation of the free tyrosine.

Aromatase, estrone sulfatase, and 17β-hydroxysteroid dehydrogenase: structure-function studies and inhibitor development

Aromatase, estrone sulfatase, and 17β-hydroxysteroid dehydrogenase type 1 are involved in the key steps of 17β-estradiol biosynthesis. Structure-function studies of aromatase, estrone sulfatase and 17β-hydroxysteroid dehydrogenase type 1 are important to evaluate the molecular basis of the interaction between these enzymes and their inhibitors. Selective and potent inhibitors of the three enzymes have been developed as antiproliferative agents in hormone-dependent breast carcinoma. New treatment strategies for hormone-dependent breast cancer are discussed.

Human sulfatases: A structural perspective to catalysis

The sulfatase family of enzymes catalyzes hydrolysis of sulfate ester bonds of a wide variety of substrates. Seventeen genes have been identified in this class of sulfatases, many of which are associated with genetic disorders leading to reduction or loss of function of the corresponding enzymes. Amino acid sequence homology suggests that the enzymes have similar overall folds, mechanisms of action, and bivalent metal ion-binding sites. A catalytic cysteine residue, strictly conserved in prokaryotic and eukaryotic sulfatases, is post-translationally modified 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 the enzyme's sulfatase activity. Crystal structures of three human sulfatases, arylsulfatases A and B(ARSA and ARSB), and estrone/dehydroepiandrosterone sulfatase or steroid sulfatase (STS), also known as arylsulfatase C, have been determined. While ARSA and ARSB are water-soluble enzymes, STS has a hydrophobic domain and is an integral membrane protein of the endoplasmic reticulum. In this article, we compare and contrast sulfatase structures and revisit the proposed catalytic mechanism in light of available structural and functional data. Examination of the STS active site reveals substrate-specific interactions previously identified as the estrogen-recognition motif. Because of the proximity of the catalytic cleft of STS to the membrane surface, the lipid bilayer has a critical role in the constitution of the active site, unlike other sulfatases.

Measuring the activities of the Sulfs: two novel heparin/heparan sulfate endosulfatases

Sulfatases hydrolyze sulfate esters on a variety of molecules including glycosaminoglycans, sulfoglycolipids, and cytosolic steroids. These enzymes are found in a wide range of organisms with their basic enzymatic mechanisms broadly conserved. In mammals, many of the sulfatases localize in the lysosome and exhibit enzymatic activity on a small aryl substrate such as 4-methylumbelliferyl sulfate (4-MUS). They are known as arylsulfatases. Sulf-1 and Sulf-2 have been cloned and identified as sulfatases that release sulfate groups on the C-6 position of GlcNAc residue from an internal subdomain in intact heparin. Hence, these enzymes are endosulfatases. The Sulfs are secreted in an active form into conditioned medium of transfected Chinese hamster ovary (CHO) cells. In this chapter, arylsulfatase and endoglucosamine-6-sulfatase assays for the Sulfs are described. A solid-phase binding assay is also detailed, which allows investigation of the ability of the Sulfs to modulate the interaction of heparin-binding proteins with immobilized heparin. The example illustrated is vascular endothelial growth factor (VEGF). This assay is projected to be very useful in the investigation of the biological functions of the Sulfs.

Probing the Origin of the Compromised Catalysis ofE.coliAlkaline Phosphatase in its Promiscuous Sulfatase Reaction

The catalytic promiscuity of E. coli alkaline phosphatase (AP) and many other enzymes provides a unique opportunity to dissect the origin of enzymatic rate enhancements via a comparative approach. Here, we use kinetic isotope effects (KIEs) to explore the origin of the 109-fold greater catalytic proficiency by AP for phosphate monoester hydrolysis relative to sulfate monoester hydrolysis. The primary 18O KIEs for the leaving group oxygen atoms in the AP-catalyzed hydrolysis of p-nitrophenyl phosphate (pNPP) and p-nitrophenylsulfate (pNPS) decrease relative to the values observed for nonenzymatic hydrolysis reactions. Prior linear free energy relationship results suggest that the transition states for AP-catalyzed reactions of phosphate and sulfate esters are "loose" and indistinguishable from that in solution, suggesting that the decreased primary KIEs do not reflect a change in the nature of the transition state but rather a strong interaction of the leaving group oxygen atom with an active site Zn2+ ion. Furthermore, the primary KIEs for the two reactions are identical within error, suggesting that the differential catalysis of these reactions cannot be attributed to differential stabilization of the leaving group. In contrast, AP perturbs the KIE for the nonbridging oxygen atoms in the reaction of pNPP but not pNPS, suggesting a differential interaction with the transferred group in the transition state. These and prior results are consistent with a strong electrostatic interaction between the active site bimetallo Zn2+ cluster and one of the nonbridging oxygen atoms on the transferred group. We suggest that the lower charge density of this oxygen atom on a transferred sulfuryl group accounts for a large fraction of the decreased stabilization of the transition state for its reaction relative to phosphoryl transfer.

Introducing genetically encoded aldehydes into proteins

Methods for introducing bioorthogonal functionalities into proteins have become central to protein engineering efforts. Here we describe a method for the site-specific introduction of aldehyde groups into recombinant proteins using the 6-amino-acid consensus sequence recognized by the formylglycine-generating enzyme. This genetically encoded 'aldehyde tag' is no larger than a His(6) tag and can be exploited for numerous protein labeling applications.

New enzymes for biotransformations: microbial alkyl sulfatases displaying stereo- and enantioselectivity

The majority of hydrolytic enzymes used in white biotechnology for the production of non-natural compounds--such as carboxyl ester hydrolases, lipases and proteases--show a certain preference for a given enantiomer. However, they are unable to alter the stereochemistry of the substrate during catalysis with respect to inversion or retention of configuration. The latter can be achieved by (alkyl) sulfatases, which can be employed for the enantio-convergent transformation of racemic sulfate esters into a single stereoisomeric secondary alcohol, with a theoretical yield of 100%. This is a major improvement over traditional kinetic resolution processes, which yield both enantiomers, each at 50%.

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.

The crystal structure of SdsA1, an alkylsulfatase from Pseudomonas aeruginosa, defines a third class of sulfatases

Pseudomonas aeruginosa is both a ubiquitous environmental bacterium and an opportunistic human pathogen. A remarkable metabolic versatility allows it to occupy a multitude of ecological niches, including wastewater treatment plants and such hostile environments as the human respiratory tract. P. aeruginosa is able to degrade and metabolize biocidic SDS, the detergent of most commercial personal hygiene products. We identify SdsA1 of P. aeruginosa as a secreted SDS hydrolase that allows the bacterium to use primary sulfates such as SDS as a sole carbon or sulfur source. Homologues of SdsA1 are found in many pathogenic and some nonpathogenic bacteria. The crystal structure of SdsA1 reveals three distinct domains. The N-terminal catalytic domain with a binuclear Zn2+ cluster is a distinct member of the metallo-beta-lactamase fold family, the central dimerization domain ensures resistance to high concentrations of SDS, whereas the C-terminal domain provides a hydrophobic groove, presumably to recruit long aliphatic substrates. Crystal structures of apo-SdsA1 and complexes with substrate analog and products indicate an enzymatic mechanism involving a water molecule indirectly activated by the Zn2+ cluster. The enzyme SdsA1 thus represents a previously undescribed class of sulfatases that allows P. aeruginosa to survive and thrive under otherwise bacteriocidal conditions.

Differential proteomic analysis of the Bacillus anthracis secretome: distinct plasmid and chromosome CO2-dependent cross talk mechanisms modulate extracellular proteolytic activities

The secretomes of a virulent Bacillus anthracis strain and of avirulent strains (cured of the virulence plasmids pXO1 and pXO2), cultured in rich and minimal media, were studied by a comparative proteomic approach. More than 400 protein spots, representing the products of 64 genes, were identified, and a unique pattern of protein relative abundance with respect to the presence of the virulence plasmids was revealed. In minimal medium under high CO(2) tension, conditions considered to simulate those encountered in the host, the presence of the plasmids leads to enhanced expression of 12 chromosome-carried genes (10 of which could not be detected in the absence of the plasmids) in addition to expression of 5 pXO1-encoded proteins. Furthermore, under these conditions, the presence of the pXO1 and pXO2 plasmids leads to the repression of 14 chromosomal genes. On the other hand, in minimal aerobic medium not supplemented with CO(2), the virulent and avirulent B. anthracis strains manifest very similar protein signatures, and most strikingly, two proteins (the metalloproteases InhA1 and NprB, orthologs of gene products attributed to the Bacillus cereus group PlcR regulon) represent over 90% of the total secretome. Interestingly, of the 64 identified gene products, at least 31 harbor features characteristic of virulence determinants (such as toxins, proteases, nucleotidases, sulfatases, transporters, and detoxification factors), 22 of which are differentially regulated in a plasmid-dependent manner. The nature and the expression patterns of proteins in the various secretomes suggest that distinct CO(2)-responsive chromosome- and plasmid-encoded regulatory factors modulate the secretion of potential novel virulence factors, most of which are associated with extracellular proteolytic activities.

Purification of a 75 kDa protein from the organelle matrix of human neutrophils and identification as N-acetylglucosamine-6-sulphatase

A 75 kDa protein was purified to homogeneity from granule extracts of normal human granulocytes using Sephadex G-75 chromatography, Mono-S cation exchange chromatography and chromatofocusing. The protein consisted of one chain with a molecular mass of 75 kDa, as determined by SDS/PAGE. Tryptic peptide analysis by MALDI-TOF (matrix-assisted laser-desorption ionization-time-of-flight) MS and sequence analysis by MS/MS identified the protein to be N-acetylglucosamine-6-sulphatase (EC 3.1.6.14). The identity of the protein was confirmed by demostrating enzymatic activity towards the substrate N-acetylglucosamine 6-sulphate. The enzyme was active over a broad pH range with an optimum of pH 7.0, and showed a K(m) value of 13.0 mM and a V(max) value of approximately 1.8 microM/min per mg. The enzyme also showed O-desulphation activity towards heparan sulphate-derived saccharides. Subcellular fractionation of neutrophil organelles showed the presence of enzymatic activity mainly in the same fractions as primary granules. Furthermore, PMA treatment of the neutrophils induced release of the enzyme, indicating its matrix protein nature. The presence of N-acetylglucosamine-6-sulphatase in human neutrophils implies that neutrophils may play a role in the modulation of cell surface molecules and extracellular matrix by O-desulphation.

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.

Fate of 3,3‘-Diindolylmethane in Cultured MCF-7 Human Breast Cancer Cells

3,3'-Diindolylmethane (DIM) is a major in vivo product of the cancer preventative agent indole-3-carbinol that is found in vegetables of the genus Brassica. Here, we report on the metabolic fate of radiolabeled DIM in MCF-7 cells. DIM was slowly metabolized to several sulfate conjugates of oxidized DIM products that were primarily detected in the medium. The radioactivity detected in cells was predominantly unmodified DIM (81-93%) at all time intervals up to 72 h treatment. Co-treatment of MCF-7 cells with quercetin slowed the rate that oxidized DIM products accumulated in the medium, while indole[3,2-b]carbazole (ICZ) co-treatment accelerated their production. ICZ is an inducer of P450 1A2, while quercetin is a specific inhibitor of this isoform, suggesting that P450 1A2 is primarily responsible for the oxidation of DIM, probably through 2,3-epoxidation similar to 3-methylindole. Sulfate conjugates of oxidized DIM metabolites were cleaved by sulfatase digestion and identified by LC/MS as 3-(1H-indole-3-ylmethyl)-2-oxindole (2-ox-DIM), bis(1H-indol-3-yl)methanol (3-methylenehydroxy-DIM), 3-[hydroxy-(1H-indol-3-yl)-methyl]-1,3-dihydro-2-oxindole (3-methylenehydroxy-2-ox-DIM), and 3-hydroxy-3-(1H-indole-3-ylmethyl)-2-oxindole (3-hydroxy-2-ox-DIM). Derivatives of 2-ox-DIM represented greater than 30% of the radioactivity in the sulfatase-digested medium. Although oxindole formation was the primary metabolic pathway in MCF-7 cells, synthetic 2-ox-DIM was inactive in a 4-ERE-luciferase reporter assay and, therefore, probably not responsible for the estrogenic activity previously observed for DIM. Unmodified DIM rapidly accumulated in the nuclear membranes representing approximately 35-40% of the radioactivity after 0.5-2 h treatment. Uptake of radiolabeled DIM appeared to be a passive partitioning into the nuclear membranes and was not dependent upon the cell cytosol. The nuclear uptake of DIM was not saturable and could not be blocked by pretreatment with unlabeled DIM (100 microM). Further, treatments in serum-free medium increased the uptake of radiolabeled DIM by the MCF-7 cells. These findings show that the uptake of DIM by membranes significantly increases its localized concentration, which may contribute to its biological activities.

An alpha-formylglycine building block for fmoc-based solid-phase peptide synthesis

[reaction: see text] Nearly all known sulfatases share a common active site modification that is required for their activity: conversion of cysteine to alpha-formylglycine. We report the synthesis of an alpha-formylglycine building block suitable for Fmoc-based solid-phase peptide synthesis. The building block was incorporated into a synthetic peptide derived from the active site of a Mycobacterium tuberculosis sulfatase.

Purification of the crude solution from Helix pomatia for use as beta-glucuronidase and aryl sulfatase in phytoestrogen assays

Phytoestrogens occur in a variety of foods and are thought to offer a protective effect against a number of complex diseases. Due to the diversity of phytoestrogen conjugates formed in the human body, most assays include an enzymatic hydrolysis step prior to analysis. beta-Glucuronidase from Helix pomatia, which also contains sulfatase activity, is popular for this task but contains appreciable levels of some phytoestrogens and related compounds, which could affect accurate quantification at low concentrations. Use of solid phase extraction on a polymeric resin has been found to remove the majority of these compounds from the enzyme, without affecting the enzyme activity for almost all of the analytes tested.

A general binding mechanism for all human sulfatases by the formylglycine-generating enzyme

The formylglycine (FGly)-generating enzyme (FGE) uses molecular oxygen to oxidize a conserved cysteine residue in all eukaryotic sulfatases to the catalytically active FGly. Sulfatases degrade and remodel sulfate esters, and inactivity of FGE results in multiple sulfatase deficiency, a fatal disease. The previously determined FGE crystal structure revealed two crucial cysteine residues in the active site, one of which was thought to be implicated in substrate binding. The other cysteine residue partakes in a novel oxygenase mechanism that does not rely on any cofactors. Here, we present crystal structures of the individual FGE cysteine mutants and employ chemical probing of wild-type FGE, which defined the cysteines to differ strongly in their reactivity. This striking difference in reactivity is explained by the distinct roles of these cysteine residues in the catalytic mechanism. Hitherto, an enzyme-substrate complex as an essential cornerstone for the structural evaluation of the FGly formation mechanism has remained elusive. We also present two FGE-substrate complexes with pentamer and heptamer peptides that mimic sulfatases. The peptides isolate a small cavity that is a likely binding site for molecular oxygen and could host reactive oxygen intermediates during cysteine oxidation. Importantly, these FGE-peptide complexes directly unveil the molecular bases of FGE substrate binding and specificity. Because of the conserved nature of FGE sequences in other organisms, this binding mechanism is of general validity. Furthermore, several disease-causing mutations in both FGE and sulfatases are explained by this binding mechanism.

Substrate specificity and domain functions of extracellular heparan sulfate 6-O-endosulfatases, QSulf1 and QSulf2

The extracellular sulfatases (Sulfs) are an evolutionally conserved family of heparan sulfate (HS)-specific 6-O-endosulfatases. These enzymes remodel the 6-O-sulfation of cell surface HS chains to promote Wnt signaling and inhibit growth factor signaling for embryonic tissue patterning and control of tumor growth. In this study we demonstrate that the avian HS endosulfatases, QSulf1 and QSulf2, exhibit the same substrate specificity toward a subset of trisulfated disaccharides internal to HS chains. Further, we show that both QSulfs associate exclusively with cell membrane and are enzymatically active on the cell surface to desulfate both cell surface and cell matrix HS. Mutagenesis studies reveal that conserved amino acid regions in the hydrophilic domains of QSulf1 and QSulf2 have multiple functions, to anchor Sulf to the cell surface, bind to HS substrates, and to mediate HS 6-O-endosulfatase enzymatic activity. Results of our current studies establish the hydrophilic domain (HD) of Sulf enzymes as an essential multifunctional domain for their unique endosulfatase activities and also demonstrate the extracellular activity of Sulfs for desulfation of cell surface and cell matrix HS in the control of extracellular signaling for embryonic development and tumor progression.

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.

Hydrolysis of Conjugated Metabolites of Buprenorphine II. The Quantitative Enzymatic Hydrolysis of Norbuprenorphine-3- -D-Glucuronide in Human Urine

In gas chromatographic-mass spectroscopic analysis of buprenorphine metabolites, the urine specimen must be first hydrolyzed to release buprenorphine and norbuprenorphine from their glucuronide conjugates. For evaluation of existing hydrolysis methods and to find out the optimal hydrolysis conditions, buprenorphine-3-beta-D-glucuronide (B3G) and norbuprenorphine-3-beta-D-glucuronide (NB3G) were synthesized. In a previous communication we reported on the optimum conditions for hydrolysis of B3G. Because we have previously shown that no hydrolysis was achieved under basic conditions and that acid hydrolysis resulted in extensive degradation, only enzymatic hydrolysis was examined for NB3G. This study therefore reports on the optimum enzymatic conditions for the hydrolysis of NB3G. Urine fortified with synthetic NB3G was hydrolyzed with beta-glucuronidases from different source species, including Helix pomatia, Escherichia coli, and Patella vulgata. Glusulase, a preparation containing both the beta-glucuronidase (H. pomatia) and sulfatase, was also tested. It was found that marked differences exist in the reactivity of these enzymes. Incubation with glucuronidases from H. pomatia or E. coli at 37 degrees C for 16 h resulted in quantitative hydrolysis of NB3G. At 60 degrees C, complete hydrolysis was achieved with 1000 units of H. pomatia in 4 h and after only 1 h with glusulase. On the other hand, incubation at 60 degrees C for 4 h with Patella vulgata resulted in only 14.7% hydrolysis.

De novocalcium/sulfur SAD phasing of the human formylglycine-generating enzyme using in-house data

Sulfatases are a family of enzymes essential for the degradation of sulfate esters. Formylglycine is the key catalytic residue in the active site of sulfatases and is generated from a cysteine residue by FGE, the formylglycine-generating enzyme. Inactivity of FGE owing to inherited mutations in the FGE gene results in multiple sulfatase deficiency (MSD), which leads to early death in infants. Human FGE was crystallized in the presence of traces of the protease elastase, which was absolutely essential for crystal growth, and the structure of FGE was determined by molecular replacement. Before this model was completed, the FGE structure was re-determined by SAD phasing using in-house data based on the anomalous signal of two calcium ions bound to the native enzyme and intrinsic S atoms. A 14-atom substructure was determined at 1.8 A resolution by SHELXD; SHELXE was used for density modification and phase extension to 1.54 A resolution. Automated model building with ARP/wARP and refinement with REFMAC5 yielded a virtually complete model without manual intervention. The minimal data requirements for successful phasing and the relative contributions of the Ca and S atoms are discussed and compared with the related FGE paralogue, pFGE. This work emphasizes the usefulness of de novo phasing using weak anomalous scatterers and in-house data.

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.

Expression, localization, structural, and functional characterization of pFGE, the paralog of the Calpha-formylglycine-generating enzyme

pFGE is the paralog of the formylglycine-generating enzyme (FGE), which catalyzes the oxidation of a specific cysteine to Calpha-formylglycine, the catalytic residue in the active site of sulfatases. The enzymatic activity of sulfatases depends on this posttranslational modification, and the genetic defect of FGE causes multiple sulfatase deficiency. The structural and functional properties of pFGE were analyzed. The comparison with FGE demonstrates that both share a tissue-specific expression pattern and the localization in the lumen of the endoplasmic reticulum. Both are retained in the endoplasmic reticulum by a saturable mechanism. Limited proteolytic cleavage at similar sites indicates that both also share a similar three-dimensional structure. pFGE, however, is lacking the formylglycine-generating activity of FGE. Although overexpression of FGE stimulates the generation of catalytically active sulfatases, overexpression of pFGE has an inhibitory effect. In vitro pFGE interacts with sulfatase-derived peptides but not with FGE. The inhibitory effect of pFGE on the generation of active sulfatases may therefore be caused by a competition of pFGE and FGE for newly synthesized sulfatase polypeptides.

Crystal structure of human pFGE, the paralog of the Calpha-formylglycine-generating enzyme

In eukaryotes, sulfate esters are degraded by sulfatases, which possess a unique Calpha-formylglycine residue in their active site. The defect in post-translational formation of the Calpha-formylglycine residue causes a severe lysosomal storage disorder in humans. Recently, FGE (formylglycine-generating enzyme) has been identified as the protein required for this specific modification. Using sequence comparisons, a protein homologous to FGE was found and denoted pFGE (paralog of FGE). pFGE binds a sulfatase-derived peptide bearing the FGE recognition motif, but it lacks formylglycine-generating activity. Both proteins belong to a large family of pro- and eukaryotic proteins containing the DUF323 domain, a formylglycine-generating enzyme domain of unknown three-dimensional structure. We have crystallized the glycosylated human pFGE and determined its crystal structure at a resolution of 1.86 A. The structure reveals a novel fold, which we denote the FGE fold and which therefore serves as a paradigm for the DUF323 domain. It is characterized by an asymmetric partitioning of secondary structure elements and is stabilized by two calcium cations. A deep cleft on the surface of pFGE most likely represents the sulfatase polypeptide binding site. The asymmetric unit of the pFGE crystal contains a homodimer. The putative peptide binding site is buried between the monomers, indicating a biological significance of the dimer. The structure suggests the capability of pFGE to form a heterodimer with FGE.

Molecular characterization of the human Calpha-formylglycine-generating enzyme

Calpha-formylglycine (FGly) is the catalytic residue in the active site of sulfatases. In eukaryotes, it is generated in the endoplasmic reticulum by post-translational modification of a conserved cysteine residue. The FGly-generating enzyme (FGE), performing this modification, is an endoplasmic reticulum-resident enzyme that upon overexpression is secreted. Recombinant FGE was purified from cells and secretions to homogeneity. Intracellular FGE contains a high mannose type N-glycan, which is processed to the complex type in secreted FGE. Secreted FGE shows partial N-terminal trimming up to residue 73 without loosing catalytic activity. FGE is a calcium-binding protein containing an N-terminal (residues 86-168) and a C-terminal (residues 178-374) protease-resistant domain. The latter is stabilized by three disulfide bridges arranged in a clamp-like manner, which links the third to the eighth, the fourth to the seventh, and the fifth to the sixth cysteine residue. The innermost cysteine pair is partially reduced. The first two cysteine residues are located in the sequence preceding the N-terminal protease-resistant domain. They can form intramolecular or intermolecular disulfide bonds, the latter stabilizing homodimers. The C-terminal domain comprises the substrate binding site, as evidenced by yeast two-hybrid interaction assays and photocross-linking of a substrate peptide to proline 182. Peptides derived from all known human sulfatases served as substrates for purified FGE indicating that FGE is sufficient to modify all sulfatases of the same species.

Estrogen Sulfatase

Estrogen sulfatase is a microsomal enzyme and is ubiquitously distributed in several mammalian tissues, among which the liver, placenta, and endocrine tissues exhibit relatively high activity. Because the major circulating precursors of estrogen are estrone 3-sulfate and dehydroepiandrosterone 3-sulfate, estrogen sulfatase plays an important role not only in their incorporation and metabolism, but also in the controls of estrogen activity by regulating the binding potential of estrogen as to its receptor through sulfoconjugation and desulfation reactions. Accordingly, an increase in sulfoconjugation through transfection of the sulfotransferase gene or inhibition of estrogen sulfatase by specific inhibitors has been successfully applied to abolish the estrogen activity in estrogen-dependent breast cancer- and uterine endometrial adenocarcinoma-derived cells. Inhibitors of estrogen sulfatase are expected to be developed as new drugs for estrogen-dependent cancer therapy, particularly in postmenopausal women.

Highly enantioselective stereo-inverting sec-alkylsulfatase activity of hyperthermophilic Archaea

rac-sec-Alkyl sulfate esters 1a-8a were resolved in low to excellent enantioselectivities with E-values up to >200 using whole cells of aerobically-grown hyperthermophilic sulfur-metabolizers, such as Sulfolobus solfataricus DSM 1617, Sulfolobus shibatae DSM 5389 and, most notably, Sulfolobus acidocaldarius DSM 639. Significantly enhanced selectivities were obtained using cells grown on sucrose-enriched Brock-medium. The stereochemical course of this biohydrolysis was shown to proceed with strict inversion of configuration, thus the preferred (R)-enantiomers were converted into the corresponding (S)-sec-alcohols to furnish a homochiral product mixture.

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.