Crystal structures of human sulfotransferases SULT1B1 and SULT1C1 complexed with the cofactor product adenosine-3'- 5'-diphosphate (PAP)

Evaluation of the Toxicity Potential of the Metabolites of Di-Isononyl Phthalate and of Their Interactions with Members of Family 1 of Sulfotransferases-A Computational Study

Di-isononyl phthalates are chemicals that are widely used as plasticizers. Humans are extensively exposed to these compounds by dietary intake, through inhalation and skin absorption. Sulfotransferases (SULTs) are enzymes responsible for the detoxification and elimination of numerous endogenous and exogenous molecules from the body. Consequently, SULTs are involved in regulating the biological activity of various hormones and neurotransmitters. The present study considers a computational approach to predict the toxicological potential of the metabolites of di-isononyl phthalate. Furthermore, molecular docking was considered to evaluate the inhibitory potential of these metabolites against the members of family 1 of SULTs. The metabolites of di-isononyl phthalate reveal a potency to cause liver damage and to inhibit receptors activated by peroxisome proliferators. These metabolites are also usually able to inhibit the activity of the members of family 1 of SULTs, except for SULT1A3 and SULT1B1. The outcomes of this study are important for an enhanced understanding of the risk of human exposure to di-isononyl phthalates.

Histone tyrosine sulfation by SULT1B1 regulates H4R3me2a and gene transcription

Tyrosine sulfation is a common posttranslational modification in mammals. To date, it has been thought to be limited to secreted and transmembrane proteins, but little is known about tyrosine sulfation on nuclear proteins. Here we report that SULT1B1 is a histone sulfotransferase that can sulfate the tyrosine 99 residue of nascent histone H3 in cytosol. The sulfated histone H3 can be transported into the nucleus and majorly deposited in the promoter regions of genes in chromatin. While the H3Y99 residue is buried inside octameric nucleosome, dynamically regulated subnucleosomal structures provide chromatin-H3Y99sulf the opportunity of being recognized and bound by PRMT1, which deposits H4R3me2a in chromatin. Disruption of H3Y99sulf reduces PRMT1 binding to chromatin, H4R3me2a level and gene transcription. These findings reveal the mechanisms underlying H3Y99 sulfation and its cross-talk with H4R3me2a to regulate gene transcription. This study extends the spectrum of tyrosine sulfation on nuclear proteins and the repertoire of histone modifications regulating chromatin functions.

Evaluation of nanoplastics toxicity to the human placenta in systems

Following the discovery of plastics in the human placenta, this study evaluated the toxicity of ten different nanoplastics (NPs) in the human placenta. Since the placenta performs metabolic and excretion functions by the enzymatic system, the NPs were docked on these human enzymes including soluble epoxide hydrolase, uracil phosphoribosyltransferase, beta 1,3-glucuronyltransferase I, sulfotransferase, N-acetyltransferase 2, and cytochrome P450 1A1at their active sites with toxicity (binding affinity) determined and compared to control compounds. Density functional theory analysis were conducted on the NPs to identify their global reactivity descriptors and Artificial Neural Networks to predict toxicity based on reactivity descriptors. Polycarbonate (PC), polyethylene terephthalate (PET) and polystyrene (PS) showed the highest toxicity to all enzymes and thus the most toxic polymers due to the presence of an electron-withdrawing group in their aromatic rings, which demonstrated an improved recognition of the enzyme active site by pi- and alkyl interactions. A 2^10-6 fractional factorial design approach was used in conjunction with a fixed effects model to assess the primary and secondary effects of NPs in a composite system on binding affinity to the placental enzymes. The simulation results suggest that NPs mixture may pose significant risks to the placenta through inhibition of its key enzymes.

From Steroid and Drug Metabolism to Glycobiology, Using Sulfotransferase Structures to Understand and Tailor Function

Sulfotransferases are ubiquitous enzymes that transfer a sulfo group from the universal cofactor donor 3'-phosphoadenosine 5'-phosphosulfate to a broad range of acceptor substrates. In humans, the cytosolic sulfotransferases are involved in the sulfation of endogenous compounds such as steroids, neurotransmitters, hormones, and bile acids as well as xenobiotics including drugs, toxins, and environmental chemicals. The Golgi associated membrane-bound sulfotransferases are involved in post-translational modification of macromolecules from glycosaminoglycans to proteins. The sulfation of small molecules can have profound biologic effects on the functionality of the acceptor, including activation, deactivation, or enhanced metabolism and elimination. Sulfation of macromolecules has been shown to regulate a number of physiologic and pathophysiological pathways by enhancing binding affinity to regulatory proteins or binding partners. Over the last 25 years, crystal structures of these enzymes have provided a wealth of information on the mechanisms of this process and the specificity of these enzymes. This review will focus on the general commonalities of the sulfotransferases, from enzyme structure to catalytic mechanism as well as providing examples into how structural information is being used to either design drugs that inhibit sulfotransferases or to modify the enzymes to improve drug synthesis. SIGNIFICANCE STATEMENT: This manuscript honors Dr. Masahiko Negishi's contribution to the understanding of sulfotransferase mechanism, specificity, and roles in biology by analyzing the crystal structures that have been solved over the last 25 years.

Combinatorial Biosynthesis of Sulfated Benzenediol Lactones with a Phenolic Sulfotransferase from Fusarium graminearum PH-1

Total biosynthesis or whole-cell biocatalytic production of sulfated small molecules relies on the discovery and implementation of appropriate sulfotransferase enzymes. Although fungi are prominent biocatalysts and have been used to sulfate drug-like phenolics, no gene encoding a sulfotransferase enzyme has been functionally characterized from these organisms. Here, we identify a phenolic sulfotransferase, FgSULT1, by genome mining from the plant-pathogenic fungus Fusarium graminearum PH-1. We expressed FgSULT1 in a Saccharomyces cerevisiae chassis to modify a broad range of benzenediol lactones and their nonmacrocyclic congeners, together with an anthraquinone, with the resulting unnatural natural product (uNP) sulfates displaying increased solubility. FgSULT1 shares low similarity with known animal and plant sulfotransferases. Instead, it forms a sulfotransferase family with putative bacterial and fungal enzymes for phase II detoxification of xenobiotics and allelochemicals. Among fungi, putative FgSULT1 homologues are encoded in the genomes of Fusarium spp. and a few other genera in nonsyntenic regions, some of which may be related to catabolic sulfur recycling. Computational structure modeling combined with site-directed mutagenesis revealed that FgSULT1 retains the key catalytic residues and the typical fold of characterized animal and plant sulfotransferases. Our work opens the way for the discovery of hitherto unknown fungal sulfotransferases and provides a synthetic biological and enzymatic platform that can be adapted to produce bioactive sulfates, together with sulfate ester standards and probes for masked mycotoxins, precarcinogenic toxins, and xenobiotics.IMPORTANCE Sulfation is an expedient strategy to increase the solubility, bioavailability, and bioactivity of nutraceuticals and clinically important drugs. However, chemical or biological synthesis of sulfoconjugates is challenging. Genome mining, heterologous expression, homology structural modeling, and site-directed mutagenesis identified FgSULT1 of Fusarium graminearum PH-1 as a cytosolic sulfotransferase with the typical fold and active site architecture of characterized animal and plant sulfotransferases, despite low sequence similarity. FgSULT1 homologues are sparse in fungi but form a distinct clade with bacterial sulfotransferases. This study extends the functionally characterized sulfotransferase superfamily to the kingdom Fungi and demonstrates total biosynthetic and biocatalytic synthetic biological platforms to produce unnatural natural product (uNP) sulfoconjugates. Such uNP sulfates may be utilized for drug discovery in human and veterinary medicine and crop protection. Our synthetic biological methods may also be adapted to generate masked mycotoxin standards for food safety and environmental monitoring applications and to expose precarcinogenic xenobiotics.

Assessment of the endocrine-disrupting effects of diethyl phosphate, a nonspecific metabolite of organophosphorus pesticides, by in vivo and in silico approaches

Organophosphorus pesticides (OPs) remain one of the most commonly used pesticides, and their detection rates and residues in agricultural products, foods and environmental samples have been underestimated. Humans and environmental organisms are at high risk of exposure to OPs. Most OPs can be degraded and metabolized into dialkyl phosphates (DAPs) in organisms and the environment, and can be present in urine as biomarkers for exposure to OPs, of which diethyl phosphate (DEP) is a high-exposure metabolite. Epidemiological and cohort studies have found that DAPs are associated with endocrine hormone disorders, especially sex hormone disorders and thyroid hormone disorders, but there has been no direct causal evidence to support these findings. Our study explored the effects of chronic exposure to DEP on endocrine hormones and related metabolic indicators in adult male rats at actual doses that can be reached in the human body. The results showed that chronic exposure to DEP could cause thyroid-related hormone disorders in the serum of rats, causing symptoms of hyperthyroidism in rats, and could also lead to abnormal expression of thyroid hormone-related genes in the rat liver. However, DEP exposure did not seem to affect serum sex hormone levels, spermatogenesis or sperm quality in rats. The molecular interactions between DEP and thyroid hormone-related enzymes/proteins were investigated by molecular docking and molecular dynamics methods in silico. It was found that DEP could strongly interact with thyroid hormone biosynthesis, blood transport, receptor binding and metabolism-related enzymes/proteins, interfering with the production and signal regulation of thyroid hormones. In vivo and in silico experiments showed that DEP might be a potential thyroid hormone-disrupting chemical, and therefore, we need to be more cautious and rigorous regarding organophosphorus chemical exposure.

A high frequency missense SULT1B1 allelic variant (L145V) selectively expressed in African descendants exhibits altered kinetic properties

1. Human cytosolic sulfotransferase 1B1 (SULT1B1) sulfates small phenolic compounds and bioactivates polycyclic aromatic hydrocarbons. To date, no SULT1B1 allelic variants have been well-characterized. 2. While cloning SULT1B1 from human endometrial specimens, an allelic variant resulting in valine instead of leucine at the 145th amino acid position (L145V) was detected. NCBI reported this alteration as the highest frequency SULT1B1 allelic variant. 3. L145V frequency comprised 9% of 37 mixed-population human patients and was specific to African Americans with an allelic frequency of 25%. Structurally, replacement of leucine with valine potentially destabilizes a conserved helix (α8) that forms the "floor" of both the substrate and PAPS binding domains. This destabilization results in altered kinetic properties including a four-fold decrease in affinity for PAP (3', 5'-diphosphoadenosine). K_ms for 3'-phosphoadenosine- 5'-phosphosulfate (PAPS) are similar; however, maximal turnover rate of the variant isoform (0.86 pmol/(min*μg)) is slower than wild-type (WT) SULT1B1 (1.26 pmol/(min*μg)). The L145V variant also displays altered kinetics toward small phenolic substrates, including a diminished p-nitrophenol K_m and increased susceptibility to 1-naphthol substrate inhibition. 4. No significant correlation between genotype and prostate or colorectal cancer was observed in patients; however, the variant isoform could underlie specific pathologies in sub-Saharan African carriers.

Expression of the sulfotransferase 1C family: implications for xenobiotic toxicity

The SULT1C enzymes are a relatively under-studied branch of the cytosolic sulfotransferase (SULT) multigene family. Concrete information about SULT1C tissue-specific expression, substrate preference, role in physiology and regulation is just emerging in the literature. The role of SULT1Cs in normal physiology is uncertain, but SULT1C-catalyzed sulfonation of thyroid hormones may be a mechanism to titrate the pre-receptor levels of biologically active thyroid hormone in target tissues. Both rat and human cytosolic SULT1Cs are most noted for their ability to bioactivate potent procarcinogens such as N-hydroxy-2-acetylaminofluorene. This implicates a possible role for the SULT1Cs as modulators of environmental carcinogen exposure and determinants of neoplastic transformation. In humans, the SULT1Cs are likely to function physiologically in cell proliferation and organogenesis pathways during development, as SULT1Cs appear to be preferentially expressed during fetal life. In recent years, the SULT1C nomenclature as presented in the literature has undergone major changes in response to updated genomic information. The purpose of this review is to summarize the current literature on the SULT1Cs and to clarify perspectives on SULT1C species differences, tissue-specific expression, nomenclature and role in pathophysiology. The ultimate goal is to understand the undiscovered impact of SULT1C expression on hormone homeostasis and xenobiotic toxicity during human development and as a prelude to disease development later in life.

Crystal structures of human sulfotransferases: insights into the mechanisms of action and substrate selectivity

INTRODUCTION

Cytosolic sulfotransferases (SULTs) are the enzymes that catalyze the sulfonation reaction, an important metabolic pathway for numerous endogenous and exogenous compounds. Human SULTs exhibit complex patterns of broad, differential and overlapping substrate selectivity. Moreover, these enzymes often display substrate inhibition kinetics (i.e., inhibition of the enzyme activity at high substrate concentrations).

AREAS COVERED

At present, the crystal structures for 12 human SULTs (i.e., SULT1A1, 1A2, 1A3, 1B1, 1C1, 1C2, 1C3, 1E1, 2A1, 2B1a, 2B1b and 4A1) are available, many of which are in complex with a substrate. This review describes the similarities and differences in these structures (particularly the active-site structures) of SULT enzymes. The authors also discuss the structural basis for understanding the catalytic mechanism, the substrate inhibition mechanisms, the cofactor (3'-phosphoadenosine 5'-phosphosulfate or PAPS) binding and the substrate recognition.

EXPERT OPINION

Correlations of the structural features (including conformational flexibility) in the active sites with the substrate profiles of several SULTs have been well established. One is encouraged to closely integrate in silico approaches with the structural knowledge of the active sites for development of a rationalized and accurate tool that is able to predict metabolism of SULTs toward chemicals and drug candidates.

Substrate inhibition kinetics in drug metabolism reactions

Inhibition of enzyme activity at high substrate concentrations, so-called "substrate inhibition," is commonly observed and has been recognized in drug metabolism reactions since the last decade. Although the importance of such "atypical" kinetics in vivo remains poorly understood, a substrate with substrate inhibition kinetics has been shown to unconventionally alter the metabolism of other substrates. In recent years, it is becoming increasingly evident that the mechanisms for substrate inhibition are highly complex, which are possibly contributed by multiple (at least two) binding sites within the enzyme protein, the formation of a ternary dead-end enzyme complex, and/or the ligand-induced changes in enzyme conformation. This review primarily discusses the mechanisms for substrate inhibition displayed by the important drug-metabolizing enzymes, such as cytochrome p450s, UDP-glucuronyltransferases, and sulfotransferases. Kinetic modeling of substrate inhibition in the absence or presence of a modifier is another central issue in this review because of its importance in the determination of kinetic parameters and in vitro/in vivo predictions.

Crystal structures of the glycopeptide sulfotransferase Teg12 in a complex with the teicoplanin aglycone

The TEG gene cluster, a glycopeptide biosynthetic gene cluster that is predicted to encode the biosynthesis of a polysulfated glycopeptide congener, was recently cloned from DNA extracted directly from desert soil. This predicted glycopeptide gene cluster contains three closely related sulfotransferases (Teg12, -13, and -14) that sulfate teicoplanin-like glycopeptides at three unique sites. Here we report a series of structures: an apo structure of Teg12, Teg12 bound to the desulfated cosubstrate 3'-phosphoadenosine 5'-phosphate, and Teg12 bound to the teicoplanin aglycone. Teg12 appears to undergo a series of significant conformational rearrangements during glycopeptide recruitment, binding, and catalysis. Loop regions that exhibit the most conformational flexibility show the least sequence conservation between TEG sulfotransferases. Site-directed mutagenesis guided by our structural studies confirmed the importance of key catalytic residues as well as the importance of residues found throughout the conformationally flexible loop regions.

Pharmacokinetic parameters and a theoretical study about metabolism of BR-AEA (a salbutamol derivative) in rabbit

In this study, we report the pharmacokinetics of 1-(4-di-hydroxy-3,5-dioxa-4-borabicyclo[4.4.0]deca-7,9,11- trien-9-yl)-2-(tert-butylamino)ethanol (BR-AEA). This compound was identified as a more potent beta(2) adrenoceptor (beta(2)AR) agonist than salbutamol. A sensitive and reproducible high-performance liquid chromatography (HPLC) method was used for determining the time-dependent BR-AEA concentration in healthy rabbit plasma. The pharmacokinetic parameters obtained are explained in relation to the compound's metabolism by sulfotransferases. For this purpose, docking simulations were carried out on SULT1A3, SULT1C1, and SULT1A1 3-D models using the Autodock 3.0.5 program. According to the HPLC results, t(1/2) = 2.36 +/- 0.18 h and K(e) = 0.32 +/- 0.02 h(-1) for BR-AEA in rabbit plasma. Thus, BR-AEA has a greater half-life compared with salbutamol (t(1/2) = 0.66 +/- 0.08 h). This could be due to the protection that the boronic acid moiety of BR-AEA offers to the hydroxyl groups that would otherwise be susceptible to sulfation when exposed inside the active site of the sulfotransferase. This could be due to the fact that BR-AEA has a high affinity for the side-chain hydroxyl groups of Ser and Tyr residues of the enzymes, which are located outside the active site.

Structural rearrangement of SULT2A1: effects on dehydroepiandrosterone and raloxifene sulfation

BACKGROUND: Human cytosoloic sulfotransferase (SULT) 2A1 is a major hepatic isoform and sulfates hydroxyl groups in structurally diverse sterols and xenobiotics. SULT2A1 crystal structures resolved in the presence and absence of 3',5'-diphosphoadenosine (PAP) or dehydropeiandrosterone (DHEA) suggest a significant rearrangement of the peptide that forms the surface of the active site in the presence of PAP. MATERIALS AND METHODS: Molecular modeling was used to examine the effects of the rearrangement in SULT2A1 associated with 3'-phosphoadenosine 5'-phosphosulfate (PAPS) binding on the binding of DHEA and raloxifene. The kinetics of DHEA and raloxifene sulfation was analyzed to investigate the effects of the rearrangement on SULT2A1 activity. RESULTS: Molecular models indicate that DHEA is able to bind to SULT2A1 in both conformations (open, without PAP; closed, with PAP) in a catalytic configuration, whereas raloxifene bound in a catalytic conformation only in the open structure. Raloxifene did not bind in the smaller, closed substrate binding pocket. Kinetic analysis of DHEA sulfation was consistent with a random Bi-Bi reaction mechanism, whereas raloxifene sulfation was more indicative of an ordered reaction mechanism with raloxifene binding first. Initial burst kinetics with DHEA yielded similar results after preincubation of SULT2A1 with DHEA or PAPS. Preincubation of SULT2A1 with raloxifene showed a burst of raloxifene sulfate formation with the addition of PAPS. In contrast, little raloxifene sulfate was formed if SULT2A1 was preincubated with PAPS and the reaction initiated with raloxifene. CONCLUSIONS: The structural rearrangements in SULT2A1 caused by PAPS binding can alter the sulfation mechanism and kinetics of different substrates.

Sulfotransferases, sulfatases and formylglycine-generating enzymes: a sulfation fascination

Sulfotransferases and sulfatases are the major enzymes responsible for sulfate transfer processes. The past two years have seen the elucidation of new functions for these enzymes, and a great progression in their structural characterization, which confirms that these two types of enzymes possess a highly conserved fold. For catalytic activity, sulfatases must contain a formylglycine residue, which is generated by various formylglycine-generating enzymes. Mechanistic and structural details have recently been obtained for a group of cofactor-independent formylglycine-generating enzymes termed FGEs. Finally, an increasing light has been cast upon the mechanism of sulfatase inactivation by a group of clinically important agents, the aryl sulfamates.

Identification and characterization of KpsS, a novel polysaccharide sulphotransferase in Mesorhizobium loti

Plants enter into symbiotic relationships with bacteria that allow survival in nutrient-limiting environments. The bacterium Mesorhizobium loti enters into a symbiosis with the legume host, Lotus japonicus, which results in the formation of novel plant structures called root nodules. The bacteria colonize the nodules, and are internalized into the cytoplasm of the plant cells, where they reduce molecular dinitrogen for the plant. Symbiosis between M. loti and L. japonicus requires bacterial synthesis of secreted and cell-surface polysaccharides. We previously reported the identification of an unusual sulphate-modified form of capsular polysaccharide (KPS) in M. loti. To better understand the physiological function of sulphated KPS, we isolated the sulphotransferase responsible for KPS sulphation from M. loti extracts, determined its amino acid sequence and identified the corresponding M. loti open reading frame, mll7563 (which we have named kpsS). We demonstrated that partially purified KpsS functions as a fucosyl sulphotransferase in vitro. Furthermore, mutants deficient for this gene exhibit a lack of KPS sulphation and a decreased rate of nodule formation on L. japonicus. Interestingly, the kpsS gene product shares no significant amino acid similarity with previously identified sulphotransferases, but exhibited sequence identity to open reading frames of unknown function in diverse bacteria that interact with eukaryotes.

Structural and chemical profiling of the human cytosolic sulfotransferases

The human cytosolic sulfotransfases (hSULTs) comprise a family of 12 phase II enzymes involved in the metabolism of drugs and hormones, the bioactivation of carcinogens, and the detoxification of xenobiotics. Knowledge of the structural and mechanistic basis of substrate specificity and activity is crucial for understanding steroid and hormone metabolism, drug sensitivity, pharmacogenomics, and response to environmental toxins. We have determined the crystal structures of five hSULTs for which structural information was lacking, and screened nine of the 12 hSULTs for binding and activity toward a panel of potential substrates and inhibitors, revealing unique "chemical fingerprints" for each protein. The family-wide analysis of the screening and structural data provides a comprehensive, high-level view of the determinants of substrate binding, the mechanisms of inhibition by substrates and environmental toxins, and the functions of the orphan family members SULT1C3 and SULT4A1. Evidence is provided for structural "priming" of the enzyme active site by cofactor binding, which influences the spectrum of small molecules that can bind to each enzyme. The data help explain substrate promiscuity in this family and, at the same time, reveal new similarities between hSULT family members that were previously unrecognized by sequence or structure comparison alone.

Crystal structure of StaL, a glycopeptide antibiotic sulfotransferase from Streptomyces toyocaensis

Over the past decade, antimicrobial resistance has emerged as a major public health crisis. Glycopeptide antibiotics such as vancomycin and teicoplanin are clinically important for the treatment of Gram-positive bacterial infections. StaL is a 3'-phosphoadenosine 5'-phosphosulfate-dependent sulfotransferase capable of sulfating the cross-linked heptapeptide substrate both in vivo and in vitro, yielding the product A47934, a unique teicoplanin-class glycopeptide antibiotic. The sulfonation reaction catalyzed by StaL constitutes the final step in A47934 biosynthesis. Here we report the crystal structure of StaL and its complex with the cofactor product 3'-phosphoadenosine 5'-phosphate. This is only the second prokaryotic sulfotransferase to be structurally characterized. StaL belongs to the large sulfotransferase family and shows higher similarity to cytosolic sulfotransferases (ST) than to the bacterial ST (Stf0). StaL has a novel dimerization motif, different from any other STs that have been structurally characterized. We have also applied molecular modeling to investigate the binding mode of the unique substrate, desulfo-A47934. Based on the structural analysis and modeling results, a series of residues was mutated and kinetically characterized. In addition to the conserved residues (Lys(12), His(67), and Ser(98)), molecular modeling, fluorescence quenching experiments, and mutagenesis studies identified several other residues essential for substrate binding and/or activity, including Trp(34), His(43), Phe(77), Trp(132), and Glu(205).