Structure and function of sulfotransferases

Proteomic analysis of Rana sylvatica reveals differentially expressed proteins in liver in response to anoxia, dehydration or freezing stress

Ectothermic animals that live in seasonally cold regions must adapt to seasonal variation and specific environmental conditions. During the winter, some amphibians hibernate on land and encounter limited environmental water, deficient oxygen, and extremely low temperatures that can cause the whole body freezing. These stresses trigger physiological and biochemical adaptations in amphibians that allow them to survive. Rana sylvatica, commonly known as the wood frog, shows excellent freeze tolerance. They can slow their metabolic activity to a near halt and endure freezing of 65-70% of their total body water as extracellular ice during hibernation, returning to normal when the temperatures rise again. To investigate the molecular adaptations of freeze-tolerant wood frogs, a comprehensive proteomic analysis was performed on frog liver tissue after anoxia, dehydration, or freezing exposures using a label-free LC-MS/MS proteomic approach. Quantitative proteomic analysis revealed that 87, 118, and 86 proteins were significantly upregulated in dehydrated, anoxic, and frozen groups, suggesting potential protective functions. The presence of three upregulated enzymes, glutathione S-transferase (GST), aldolase (ALDOA), and sorbitol dehydrogenase (SORD), was also validated. For all enzymes, the specific enzymatic activity was significantly higher in the livers of frozen and anoxic groups than in the controls. This study reveals that GST, ALDOA, and SORD might participate in the freeze tolerance mechanism by contributing to regulating cellular detoxification and energy metabolism.

Crystal structure of activating sulfotransferase SgdX2 involved in biosynthesis of secondary metabolite sungeidine

Microorganisms synthesize a plethora of complex secondary metabolites, many of which are beneficial to human health, such as anticancer agents and antibiotics. Among these, the Sungeidines are a distinct class of secondary metabolites known for their bulky and intricate structures. They are produced by a specific biosynthetic gene cluster within the genome of the soil-dwelling actinomycete Micromonospora sp. MD118. A notable enzyme in the Sungeidine biosynthetic pathway is the activating sulfotransferase SgdX2. In this pathway, SgdX2 mediates a key sulfation step, after which the product undergoes spontaneous dehydration to yield a Sungeidine compound. To delineate the structural basis for SgdX2's substrate recognition and catalytic action, we have determined the crystal structure of SgdX2 in complex with its sulfate donor product, 3'-phosphoadenosine 5'-phosphate (PAP), at a resolution of 1.6 Å. Although SgdX2 presents a compact overall structure, its core elements are conserved among other activating sulfotransferases. Our structural analysis reveals a unique substrate-binding pocket that accommodates bulky, complex substrates, suggesting a specialized adaptation for Sungeidine synthesis. Moreover, we have constructed a substrate docking model that provides insights into the molecular interactions between SgdX2 and Sungeidine F, enhancing our understanding of the enzyme's specificity and catalytic mechanism. The model supports a general acid-base catalysis mechanism, akin to other sulfotransferases, and underscores the minor role of disordered regions in substrate recognition. This integrative study of crystallography and computational modeling advances our knowledge of microbial secondary metabolite biosynthesis and may facilitate the development of novel biotechnological applications.

A Novel Fluorescence-Based Microplate Assay for High-Throughput Screening of hSULT1As Inhibitors

Human sulfotransferase 1As (hSULT1As) play a crucial role in the metabolic clearance and detoxification of a diverse range of endogenous and exogenous substances, as well as in the bioactivation of some procarcinogens and promutagens. Pharmacological inhibiting hSULT1As activities may enhance the in vivo effects of most hSULT1As drug substrates and offer protective strategies against the hSULT1As-mediated bioactivation of procarcinogens. To date, a fluorescence-based high-throughput assay for the efficient screening of hSULT1As inhibitors has not yet been reported. In this work, a fluorogenic substrate (HN-241) for hSULT1As was developed through scaffold-seeking and structure-guided molecular optimization. Under physiological conditions, HN-241 could be readily sulfated by hSULT1As to form HN-241 sulfate, which emitted brightly fluorescent signals around 450 nm. HN-241 was then used for establishing a novel fluorescence-based microplate assay, which strongly facilitated the high-throughput screening of hSULT1As inhibitors. Following the screening of an in-house natural product library, several polyphenolic compounds were identified with anti-hSULT1As activity, while pectolinarigenin and hinokiflavone were identified as potent inhibitors against three hSULT1A isozymes. Collectively, a novel fluorescence-based microplate assay was developed for the high-throughput screening and characterization of hSULT1As inhibitors, which offered an efficient and facile approach for identifying potent hSULT1As inhibitors from compound libraries.

In Silico Structural Modeling and Binding Site Analysis of Cerebroside Sulfotransferase (CST): A Therapeutic Target for Developing Substrate Reduction Therapy for Metachromatic Leukodystrophy

Cerebroside sulfotransferase (CST) is emerging as an important therapeutic target to develop substrate reduction therapy (SRT) for metachromatic leukodystrophy (MLD), a rare neurodegenerative lysosomal storage disorder. MLD develops with progressive impairment and destruction of the myelin sheath as a result of accumulation of sulfatide around the nerve cells in the absence of its recycling mechanism with deficiency of arylsulfatase A (ARSA). Sulfatide is the product of the catalytic action of cerebroside sulfotransferase (CST), which needs to be regulated under pathophysiological conditions by inhibitor development. To carry out in silico-based preliminary drug screening or for designing new drug candidates, a high-quality three-dimensional (3D) structure is needed in the absence of an experimentally derived three-dimensional crystal structure. In this study, a 3D model of the protein was developed using a primary sequence with the SWISS-MODEL server by applying the top four GMEQ score-based templates belonging to the sulfotransferase family as a reference. The 3D model of CST highlights the features of the protein responsible for its catalytic action. The CST model comprises five β-strands, which are flanked by ten α-helices from both sides as well as form the upside cover of the catalytic pocket of CST. CST has two catalytic regions: PAPS (-sulfo donor) binding and galactosylceramide (-sulfo acceptor) binding. The catalytic action of CST was proposed via molecular docking and molecular dynamic (MD) simulation with PAPS, galactosylceramide (GC), PAPS-galactosylceramide, and PAP. The stability of the model and its catalytic action were confirmed using molecular dynamic simulation-based trajectory analysis. CST response against the inhibition potential of the experimentally reported competitive inhibitor of CST was confirmed via molecular docking and molecular dynamics simulation, which suggested the suitability of the CST model for future drug discovery to strengthen substrate reduction therapy for MLD.

A new type of sulfation reaction: C-sulfonation for α,β-unsaturated carbonyl groups by a novel sulfotransferase SULT7A1

Cytosolic sulfotransferases (SULTs) are cytosolic enzymes that catalyze the transfer of sulfonate group to key endogenous compounds, altering the physiological functions of their substrates. SULT enzymes catalyze the O-sulfonation of hydroxy groups or N-sulfonation of amino groups of substrate compounds. In this study, we report the discovery of C-sulfonation of α,β-unsaturated carbonyl groups mediated by a new SULT enzyme, SULT7A1, and human SULT1C4. Enzymatic assays revealed that SULT7A1 is capable of transferring the sulfonate group from 3'-phosphoadenosine 5'-phosphosulfate to the α-carbon of α,β-unsaturated carbonyl-containing compounds, including cyclopentenone prostaglandins as representative endogenous substrates. Structural analyses of SULT7A1 suggest that the C-sulfonation reaction is catalyzed by a novel mechanism mediated by His and Cys residues in the active site. Ligand-activity assays demonstrated that sulfonated 15-deoxy prostaglandin J2 exhibits antagonist activity against the prostaglandin receptor EP2 and the prostacyclin receptor IP. Modification of α,β-unsaturated carbonyl groups via the new prostaglandin-sulfonating enzyme, SULT7A1, may regulate the physiological function of prostaglandins in the gut. Discovery of C-sulfonation of α,β-unsaturated carbonyl groups will broaden the spectrum of potential substrates and physiological functions of SULTs.

Crystal structure of tick tyrosylprotein sulfotransferase reveals the activation mechanism of the tick anticoagulant protein madanin

Ticks pose a substantial public health risk as they transmit various pathogens. This concern is related to the adept blood-sucking strategy of ticks, underscored by the action of the anticoagulant, madanin, which is known to exhibit an approximately 1000-fold increase in anticoagulant activity following sulfation of its two tyrosine residues, Tyr51 and Tyr54. Despite this knowledge, the molecular mechanism underlying sulfation by tick tyrosylprotein sulfotransferase (TPST) remains unclear. In this study, we successfully prepared tick TPST as a soluble recombinant enzyme. We clarified the method by which this enzyme proficiently sulfates tyrosine residues in madanin. Biochemical analysis using a substrate peptide based on madanin and tick TPST, along with the analysis of the crystal structure of the complex and docking simulations, revealed a sequential sulfation process. Initial sulfation at the Tyr51 site augments binding, thereby facilitating efficient sulfation at Tyr54. Beyond direct biochemical implications, these findings considerably improve our understanding of tick blood-sucking strategies. Furthermore, combined with the utility of modified tick TPST, our findings may lead to the development of novel anticoagulants, promising avenues for thrombotic disease intervention and advancements in the field of public health.

Molybdenum nanoparticles as a potential topical medication for alopecia treatment through antioxidant pathways that differ from minoxidil

BACKGROUND

Hair loss is a common dermatological condition including various types such as alopecia areata, androgenetic alopecia, etc. Minoxidil is a topical medication used for treating hair loss, which is effective for various types of alopecia. However, minoxidil has limitations in treating hair loss, such as slow onset of action and low efficacy, and it cannot effectively inhibit one of the major pathogenic factors of hair loss - excessive oxidative stress.

METHODS

Transition metal elements with rapid electron transfer, such as molybdenum, have been extensively studied and applied for inhibiting oxidative stress. We established a mouse model for hair growth and intervened with nano-sized molybdenum, minoxidil, and a combination of both. The physicochemical properties of nano-sized molybdenum enabled it to mediate oxidative stress more quickly.

RESULTS

The results showed that nano-sized molybdenum can accelerate hair growth, increase the number of local hair follicles, and reduce the expression of oxidative stress-related molecules such as iNOS, COX2, and androgen receptors. The combination of nano-sized molybdenum and minoxidil showed an additive effect in promoting hair growth.

CONCLUSION

Our findings suggest that nano-sized molybdenum might be a potential topical medication for treating hair loss by inhibiting the oxidative stress pathway. Nano-sized molybdenum, alone or in combination with minoxidil, could be a promising therapeutic approach for patients with hair loss, particularly those who do not respond well to current treatments. Further clinical studies are warranted to confirm the efficacy and safety of this novel treatment.

Identification of novel proteins regulating lipid droplet biogenesis in filamentous fungi

Lipid droplets (LDs) are storage organelles for neutral lipids which are critical for lipid homeostasis. Current knowledge of fungal LD biogenesis is largely limited to budding yeast, while LD regulation in multinucleated filamentous fungi which exhibit considerable metabolic activity remains unexplored. In this study, 19 LD-associated proteins were identified in the multinucleated species Aspergillus oryzae using a colocalization screening of a previously established enhanced green fluorescent protein (EGFP) fusion library. Functional screening identified 12 lipid droplet-regulating (LDR) proteins whose loss of function resulted in irregular LD biogenesis, particularly in terms of LD number and size. Bioinformatics analysis, targeted mutagenesis, and microscopy revealed four LDR proteins that localize to LD via the putative amphipathic helices (AHs). Further analysis revealed that LdrA with an Opi1 domain is essential for cytoplasmic and nuclear LD biogenesis involving a novel AH. Phylogenetic analysis demonstrated that the patterns of gene evolution were predominantly based on gene duplication. Our study identified a set of novel proteins involved in the regulation of LD biogenesis, providing unique molecular and evolutionary insights into fungal lipid storage.

Contaminants from dredged sediments alter the transcriptome of Manila clam and induce shifts in microbiota composition

BACKGROUND

The reuse of dredged sediments in ports and lagoons is a big issue as it should not affect the quality and the equilibrium of ecosystems. In the lagoon of Venice, sediment management is of crucial importance as sediments are often utilized to built-up structures necessary to limit erosion. However, the impact of sediment reuse on organisms inhabiting this delicate area is poorly known. The Manila clam is a filter-feeding species of high economic and ecological value for the Venice lagoon experiencing a drastic decline in the last decades. In order to define the molecular mechanisms behind sediment toxicity, we exposed clams to sediments sampled from different sites within one of the Venice lagoon navigable canals close to the industrial area. Moreover, we investigated the impacts of dredged sediments on clam's microbial communities.

RESULTS

Concentrations of the trace elements and organic chemicals showed increasing concentrations from the city of Venice to sites close to the industrial area of Porto Marghera, where PCDD/Fs and PCBs concentrations were up to 120 times higher than the southern lagoon. While bioaccumulation of organic contaminants of industrial origin reflected sediments' chemical concentrations, metal bioaccumulation was not consistent with metal concentrations measured in sediments probably due to the activation of ABC transporters. At the transcriptional level, we found a persistent activation of the mTORC1 signalling pathway, which is central in the coordination of cellular responses to chemical stress. Microbiota characterization showed the over-representation of potential opportunistic pathogens following exposure to the most contaminated sediments, leading to host immune response activation. Despite the limited acquisition of new microbial species from sediments, the latter play an important role in shaping Manila clam microbial communities.

CONCLUSIONS

Sediment management in the Venice lagoon will increase in the next years to maintain and create new canals as well as to allow the operation of the new mobile gates at the three Venice lagoon inlets. Our data reveal important transcriptional and microbial changes of Manila clams after exposure to sediments, therefore reuse of dredged sediments represents a potential risk for the conservation of this species and possibly for other organisms inhabiting the Venice lagoon.

Crystal structure of Arabidopsis thaliana sulfotransferase SOT16 involved in glucosinolate biosynthesis

Glucosinolates (GSLs), a class of secondary metabolites found in Brassicaceae plants, play important roles in plant defense and contribute distinct flavors and aromas when used as food ingredients. Following tissue damage, GSLs undergo enzymatic hydrolysis to release bioactive volatile compounds. Understanding GSL biosynthesis and enzyme involvement is crucial for improving crop quality and advancing agriculture. Plant sulfotransferases (SOTs) play a key role in the final step of GSL biosynthesis by transferring sulfate groups to the precursor molecules. In the present study, we investigated the enzymatic reaction mechanism and broad substrate specificity of Arabidopsis thaliana sulfotransferase AtSOT16, which is involved in GSL biosynthesis, using crystal structure analysis. Our analysis revealed the specific catalytic residues involved in the sulfate transfer reaction and supported the hypothesis of a concerted acid-base catalytic mechanism. Furthermore, the docking models showed a strong correlation between the substrates with high predicted binding affinities and those experimentally reported to exhibit high activity. These findings provide valuable insights into the enzymatic reaction mechanisms and substrate specificity of GSL biosynthesis. The information obtained in this study may contribute to the development of novel strategies for manipulating GSL synthesis pathways in Brassica plants and has potential agricultural applications.

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.

Transcriptome characterization of gonadal sex differentiation in Pacific bluefin tuna, Thunnus orientalis (Temminck et Schlegel)

Tunas (genus Thunnus) are one of the most ecologically and commercially important fish worldwide. To establish a biological basis for reproduction in this globally essential species, we have recently studied crucial reproductive aspects of the Pacific bluefin tuna (T. orientalis; PBT), as a model of tuna species, based on our closed-cycle aquaculture technology. In this study, we clarified the global expression profile of the genes regulating gonadal sex differentiation in PBT, as this developmental process is vital to sexual reproduction. Based on the results of our comparative (RNA-sequencing) and temporal (qRT-PCR) transcriptome analyses using the updated genome dataset, we propose the molecular mechanisms of gonadal sex differentiation in PBT. In female gonads, foxl2 and cyp19a1a (coding aromatase) are expressed at the onset of sex differentiation. Active aromatase-mediated estrogen biosynthesis, which includes positive regulation of cyp19a1a expression by Foxl2, induces ovarian differentiation. By contrast, dmrt1 and gsdf are upregulated in differentiating male gonads lacking active estrogen synthesis. Dmrt1 and Gsdf would mainly promote testicular differentiation. Furthermore, androgen biosynthesis is upregulated in differentiating male gonad. Endogenous androgens may also be vital to testicular differentiation. This study provides the first comprehensive data clarifying the molecular basis for gonadal sex differentiation in tunas.

The Post-Translational Modifications of Human Salivary Peptides and Proteins Evidenced by Top-Down Platforms

In this review, we extensively describe the main post-translational modifications that give rise to the multiple proteoforms characterized to date in the human salivary proteome and their potential role. Most of the data reported were obtained by our group in over twenty-five years of research carried out on human saliva mainly by applying a top-down strategy. In the beginning, we describe the products generated by proteolytic cleavages, which can occur before and after secretion. In this section, the most relevant families of salivary proteins are also described. Next, we report the current information concerning the human salivary phospho-proteome and the limited news available on sulfo-proteomes. Three sections are dedicated to the description of glycation and enzymatic glycosylation. Citrullination and N- and C-terminal post-translational modifications (PTMs) and miscellaneous other modifications are described in the last two sections. Results highlighting the variation in the level of some proteoforms in local or systemic pathologies are also reviewed throughout the sections of the manuscript to underline the impact and relevance of this information for the development of new diagnostic biomarkers useful in clinical practice.

Human cytosolic steroid sulfotransferases: Versatile and rapid activity assays

Conjugation of steroids and sterol compounds with a sulfonate group is a major pathway in the regulation of their activity, synthesis and excretion. Three human cytosolic sulfotransferases are highly involved in the sulfonation of sterol compounds. SULT1E1 has a low nM affinity for estrogen sulfonation and also conjugates non-aromatic steroids with a significantly lower affinity. SULT2A1 is responsible for the high levels of fetal and adult dehydroepiandrosterone (DHEA) sulfate synthesis in the adrenal gland as well as many 3α and 3ß-hydroxysteroids and bile acids. SULT2B1b is responsible for the majority of cholesterol sulfation in tissues as well as conjugating 3ß-hydroxysteroids. Although there are multiple methods for assaying cytosolic SULT activity, two relatively simple, rapid and versatile assays for steroid sulfonation are described. The first method utilizes radiolabeled substrates and organic solvent extraction to isolate the radiolabeled product from the aqueous phase. The second assay utilizes 35S-3'-phosphoadenosine 5'-phosphosulfate (PAPS) to generate 35S-conjugated products that are resolved by thin layer chromatography. Both assays useful in situations requiring measurement of SULT activity in a timely manner.

Predicting Regioselectivity of Cytosolic Sulfotransferase Metabolism for Drugs

Cytosolic sulfotransferases (SULTs) are a family of enzymes responsible for the sulfation of small endogenous and exogenous compounds. SULTs contribute to the conjugation phase of metabolism and share substrates with the uridine 5'-diphospho-glucuronosyltransferase (UGT) family of enzymes. UGTs are considered to be the most important enzymes in the conjugation phase, and SULTs are an auxiliary enzyme system to them. Understanding how the regioselectivity of SULTs differs from that of UGTs is essential from the perspective of developing novel drug candidates. We present a general ligand-based SULT model trained and tested using high-quality experimental regioselectivity data. The current study suggests that, unlike other metabolic enzymes in the modification and conjugation phases, the SULT regioselectivity is not strongly influenced by the activation energy of the rate-limiting step of the catalysis. Instead, the prominent role is played by the substrate binding site of SULT. Thus, the model is trained only on steric and orientation descriptors, which mimic the binding pocket of SULT. The resulting classification model, which predicts whether a site is metabolized, achieved a Cohen's kappa of 0.71.

Significant impact of redox regulation of estrogen-metabolizing proteins on cellular stress responses

The ultimate driving force, stress, promotes adaptability/evolution in proliferating organisms, transforming tumorigenic growth. Estradiol (E2) regulates both phenomena. In this study, bioinformatics-tools, site-directed-mutagenesis (human estrogen-sulfotransferase/hSULT1E1), HepG2 cells tested with N-acetyl-cysteine (NAC/thiol-inducer) or buthionine-sulfoxamine (BSO/thiol-depletory) were evaluated for hSULT1E1 (estradiol-sulphating/inactivating) functions. Reciprocal redox regulation of steroid sulfatase (STS, E2-desulfating/activating) results in the Cys-formylglycine transition by the formylglycine-forming enzyme (FGE). The enzyme sequences and structures were examined across the phylogeny. Motif/domain and the catalytic conserve sequences and protein-surface-topography (CASTp) were investigated. The E2 binding to SULT1E1 suggests that the conserved-catalytic-domain in this enzyme has critical Cysteine 83 at position. This is strongly supported by site-directed mutagenesis/HepG2-cell research. Molecular-docking and superimposition studies of E2 with the SULT1E1 of representative species and to STS reinforce this hypothesis. SULT1E1-STS are reciprocally activated in response to the cellular-redox-environment by the critical Cys of these two enzymes. The importance of E2 in organism/species proliferation and tissue tumorigenesis is highlighted.

Crystal structure of adenosine 5'-phosphosulfate kinase isolated from Archaeoglobus fulgidus

The 3'-phosphoadenosine-5'-phosphosulfate (PAPS) molecule is essential during enzyme-catalyzed sulfation reactions as a sulfate donor and is an intermediate in the reduction of sulfate to sulfite in the sulfur assimilation pathway. PAPS is produced through a two-step reaction involving ATP sulfurylase and adenosine 5'-phosphosulfate (APS) kinase enzymes/domains. However, archaeal APS kinases have not yet been characterized and their mechanism of action remains unclear. Here, we first structurally characterized APS kinase from the hyperthermophilic archaeon Archaeoglobus fulgidus, (AfAPSK). We demonstrated the PAPS production activity of AfAPSK at the optimal growth temperature (83 °C). Furthermore, we determined the two crystal structures of AfAPSK: ADP complex and ATP analog adenylyl-imidodiphosphate (AMP-PNP)/Mg2+/APS complex. Structural and complementary mutational analyses revealed the catalytic and substrate recognition mechanisms of AfAPSK. This study also hints at the molecular basis behind the thermal stability of AfAPSK.

Clustered Regularly Interspaced Short Palindromic Repeats/ CRISPR associated protein 9-mediated editing of Schistosoma mansoni genes: Identifying genes for immunologically potent drug and vaccine development

Schistosomiasis is a neglected acute and chronic tropical disease caused by intestinal (Schistosoma mansoni and Schistosoma japonicum) and urogenital (Schistosoma haematobium) helminth parasites (blood flukes or digenetic trematodes). It afflicts over 250 million people worldwide, the majority of whom reside in impoverished tropical and subtropical regions in sub-Saharan Africa. Schistosomiasis is the second most common devastating parasitic disease in the world after malaria and causes over 200,000 deaths annually. Currently, there is no effective and approved vaccine available for human use, and treatment strongly relies on praziquantel drug therapy, which is ineffective in killing immature larval schistosomula stages and eggs already lodged in the tissues. The Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR associated protein 9 (CRISPR/Cas9)-mediated gene editing tool is used to deactivate a gene of interest to scrutinize its role in health and disease, and to identify genes for vaccine and drug targeting. The present review aims to summarize the major findings from the current literature reporting the usage of CRISPR/Cas9-mediated gene editing to inactivate genes in S. mansoni (acetylcholinesterase (AChE), T2 ribonuclease omega-1 (ω1), sulfotransferase oxamniquine resistance protein (SULT-OR), and α-N-acetylgalactosaminidase (SmNAGAL)), and freshwater gastropod snails, Biomphalaria glabrata (allograft inflammatory factor (BgAIF)), an obligatory component of the life cycle of S. mansoni, to identify their roles in the pathogenesis of schistosomiasis, and to highlight the importance of such studies in identifying and developing drugs and vaccines with high therapeutic efficacy.

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.

Sulfotyrosine residues: interaction specificity determinants for extracellular protein-protein interactions

Tyrosine sulfation, a post-translational modification, can determine and often enhance protein–protein interaction specificity. Sulfotyrosyl residues (sTyrs) are formed by the enzyme tyrosyl-protein sulfotransferase during protein maturation in the Golgi apparatus and most often occur singly or as a cluster within a six-residue span. With both negative charge and aromatic character, sTyr facilitates numerous atomic contacts as visualized in binding interface structural models, thus there is no discernible binding site consensus. Found exclusively in secreted proteins, in this review, we discuss the four broad sequence contexts in which sTyr has been observed: first, a solitary sTyr has been shown to be critical for diverse high-affinity interactions, such as between peptide hormones and their receptors, in both plants and animals. Second, sTyr clusters within structurally flexible anionic segments are essential for a variety of cellular processes, including coreceptor binding to the HIV-1 envelope spike protein during virus entry, chemokine interactions with receptors, and leukocyte rolling cell adhesion. Third, a subcategory of sTyr clusters is found in conserved acidic sequences termed hirudin-like motifs that enable proteins to interact with thrombin; consequently, many proven and potential therapeutic proteins derived from blood-consuming invertebrates depend on sTyrs for their activity. Finally, several proteins that interact with collagen or similar proteins contain one or more sTyrs within an acidic residue array. Refined methods to direct sTyr incorporation in peptides synthesized both in vitro and in vivo, together with continued advances in mass spectrometry and affinity detection, promise to accelerate discoveries of sTyr occurrence and function.

Advances in the design of new types of inhaled medicines

Inhalation of small molecule drugs has proven very efficacious for the treatment of respiratory diseases due to enhanced efficacy and a favourable therapeutic index compared with other dosing routes. It enables targeted delivery to the lung with rapid onset of therapeutic action, low systemic drug exposure, and thereby reduced systemic side effects. An increasing number of pharmaceutical companies and biotechs are investing in new modalities-for this review defined as therapeutic molecules with a molecular weight >800Da and therefore beyond usual inhaled small molecule drug-like space. However, our experience with inhaled administration of PROTACs, peptides, oligonucleotides (antisense oligonucleotides, siRNAs, miRs and antagomirs), diverse protein scaffolds, antibodies and antibody fragments is still limited. Investigating the retention and metabolism of these types of molecules in lung tissue and fluid will contribute to understanding which are best suited for inhalation. Nonetheless, the first such therapeutic molecules have already reached the clinic. This review will provide information on the physiology of healthy and diseased lungs and their capacity for drug metabolism. It will outline the stability, aggregation and immunogenicity aspects of new modalities, as well as recap on formulation and delivery aspects. It concludes by summarising clinical trial outcomes with inhaled new modalities based on information available at the end of 2021.

Desorption Electrospray Ionization Mass Spectrometry Assay for Label-Free Characterization of SULT2B1b Enzyme Kinetics

The sulfotransferase (SULT) 2B1b, which catalyzes the sulfonation of 3β-hydroxysteroids, has been identified as a potential target for prostate cancer treatment. However, a major limitation for SULT2B1b-targeted drug discovery is the lack of robust assays compatible with high-throughput screening and inconsistency in reported kinetic data. For this reason, we developed a novel label-free assay based on high-throughput (>1 Hz) desorption electrospray ionization mass spectrometry (DESI-MS) for the direct quantitation of the sulfoconjugated product (CV<10 %; <1 ng analyte). The performance of this DESI-based assay was compared against a new fluorometric coupled-enzyme method that we also developed. Both methodologies provided consistent kinetic data for the reaction of SULT2B1b with its major substrates, indicating the affinity trend pregnenolone>DHEA>cholesterol, for both the phospho-mimetic and wild-type SULT2B1b forms. The novel DESI-MS assay developed here is likely generalizable to other drug discovery efforts and is particularly promising for identification of SULT2B1b inhibitors with potential as prostate cancer therapeutics.

Fluorinated Phosphoadenosine 5'-Phosphosulfate Analogues for Continuous Sulfotransferase Activity Monitoring and Inhibitor Screening by 19F NMR Spectroscopy

Sulfotransferases (STs) are ubiquitous enzymes that participate in a vast number of biological processes involving sulfuryl group (SO₃) transfer. 3′-phosphoadenosine 5′-phosphosulfate (PAPS) is the universal ST cofactor, serving as the “active sulfate” source in cells. Herein, we report the synthesis of three fluorinated PAPS analogues that bear fluorine or trifluoromethyl substituents at the C2 or C8 positions of adenine and their evaluation as substitute cofactors that enable ST activity to be quantified and real-time-monitored by fluorine-19 nuclear magnetic resonance (¹⁹F NMR) spectroscopy. Using plant AtSOT18 and human SULT1A3 as two model enzymes, we reveal that the fluorinated PAPS analogues show complementary properties with regard to recognition by enzymes and the working ¹⁹F NMR pH range and are attractive versatile tools for studying STs. Finally, we developed an ¹⁹F NMR assay for screening potential inhibitors against SULT1A3, thereby highlighting the possible use of fluorinated PAPS analogues for the discovery of drugs for ST-related diseases.

QM/MM study on enzymatic mechanism in sinigrin biosynthesis

As the major and abundant type of glucosinolates (GL) in plants, sinigrin has potential functions in promoting health and insect defense. The final step in the biosynthesis of sinigrin core structure is highly representative in GL compounds, which corresponds to the process from 3-methylthiopropyl ds-GL to 3-methylthiopropyl GL catalyzed by sulfotransferase (SOT). However, due to the lack of the crystallographic structure of SOT complexed with the 3-methylthiopropyl GL, little is known about this sulfonation process. Fortunately, the crystal structure of SOT 18 from Arabidopsis thaliana (AtSOT18) containing the substance (sinigrin) similar to 3-methylthiopropyl GL has been determined. To understand the enzymatic mechanism, we employed molecular dynamics (MD) simulation and quantum mechanics combined with molecular mechanics (QM/MM) methods to study the conversion from ds-sinigrin to sinigrin catalyzed by AtSOT18. The calculated results demonstrate that the reaction occurs through a concerted dissociative mechanism. Moreover, Lys93, Thr96, Thr97, Tyr130, His155, and two enzyme peptide chains (Pro92-Lys93 and Gln95-Thr96-Thr97) play a role in positioning the substrates and promoting the catalytic reaction by stabilizing the transition state geometry. Particularly, His155 acts as a catalytic base while Lys93 acts as a catalytic acid in the reaction process. The presently proposed concerted dissociative mechanism explains the role of AtSOT18 in sinigrin biosynthesis, and could be instructive for the study of GL biosynthesis catalyzed by other SOTs.

Long-term exposure of Daphnia magna to polystyrene microplastic (PS-MP) leads to alterations of the proteome, morphology and life-history

In the past years, the research focus on the effects of MP on aquatic organisms extended from marine systems towards freshwater systems. An important freshwater model organism in the MP field is the cladoceran Daphnia, which plays a central role in lacustrine ecosystems and has been established as a test organism in ecotoxicology. To investigate the effects of MP on Daphnia magna, we performed a chronic exposure experiment with polystyrene MP under strictly standardized conditions. Chronic exposure of D. magna to PS microparticles led to a significant reduction in body length and number of offspring. To shed light on underlying molecular mechanisms induced by microplastic ingestion in D. magna, we assessed the effects of PS-MP at the proteomic level, as proteins, e.g., enzymes, are especially relevant for an organism's physiology. Using a state-of-the-art mass spectrometry based approach, we were able to identify 28,696 different peptides, which could be assigned to 3784 different proteins. Using a customized bioinformatic workflow, we identified 41 proteins significantly altered in abundance (q-value <0.05) in the PS exposed D. magna. Among the proteins increased in the PS treated group were several sulfotransferases, involved in basic biochemical pathways, as well as GABA transaminase catalyzing the degradation of the neurotransmitter GABA. In the abundance decreased group, we found essential proteins such as the DNA-directed RNA polymerase subunit and other proteins connected to biotic and inorganic stress and reproduction. Strikingly, we further identified several digestive enzymes that are significantly downregulated in the PS treated animals, which could have interfered with the affected animal's nutrient supply. This may explain the altered morphological and life history traits of the PS exposed daphnids. Our results indicate that long-term exposure to PS microplastics, which are frequently detected in environmental samples, may affect the fitness of daphnids.

Changes in Porcine Corpus Luteum Proteome Associated with Development, Maintenance, Regression, and Rescue during Estrous Cycle and Early Pregnancy

Corpus luteum (CL), a transitory gland, undergoes rapid growth in a limited time to produce progesterone (P4) followed by its regression. A complex molecular signaling is involved in controlling luteal P4 production. In the present study, 2D gel electrophoresis-based proteomics and in silico functional analysis were used to identify changes in key proteins and pathways in CL along the different stages of the estrous cycle as its development progresses from early (Day 3) to mid-luteal phase (Day 9), effective functioning (Day 12) followed by regression (Day 15) or, in the case of pregnancy, rescue of function (Day 15). A total of 273 proteins were identified by MALDI-MS/MS analysis that showed significant changes in abundances at different stages of CL development or regression and rescue. Functional annotation of differentially abundant proteins suggested enrichment of several important pathways and functions during CL development and function maintenance including cell survival, endocytosis, oxidative stress response, estradiol metabolism, and angiogenesis. On the other hand, differentially abundant proteins during CL regression were associated with decreased steroid synthesis and metabolism and increased apoptosis, necrosis, and infiltration of immune cells. Establishment of pregnancy rescues CL from regression by maintaining the expression of proteins that support steroidogenesis as pathways such as the super-pathway of cholesterol biosynthesis, RhoA signaling, and functions such as fatty acid metabolism and sterol transport were enriched in CL of pregnancy. In this study, some novel proteins were identified along CL development that advances our understanding of CL survival and steroidogenesis.

Molecular cloning and characterization of common marmoset SULT1C subfamily members that catalyze the sulfation of thyroid hormones

Cytosolic sulfotransferase SULT1C subfamily is one of the most flexible gene subfamilies during mammalian evolution. The physiological functions of SULT1C enzymes still remain to be fully understood. In this study, common marmoset (Callithrix jacchus), a promising primate animal model, was used to investigate the functional relevance of the SULT1C subfamily. Gene database search revealed 3 intact SULT1C genes and a pseudogene in its genome. These 4 genes were named SULT1C1, SULT1C2, SULT1C3P, and SULT1C5, according to the sequence homology and gene location. Since SULT1C5 is the orthologous gene for human SULT1C2P, we propose, here, to revisit the designation of human SULT1C2P to SULT1C5P. Purified recombinant SULT1C enzymes showed sulfating activities toward a variety of xenobiotic compounds and thyroid hormones. Kinetic analysis revealed high catalytic activities of SULT1C1 and SULT1C5 for 3,3'-T2. It appears therefore that SULT1C isoforms may play a role in the thyroid hormone metabolism in common marmoset.

Phytochemical and Over-The-Counter Drug Interactions: Involvement of Phase I and II Drug-Metabolizing Enzymes and Phase III Transporters

Consumption of plant-derived natural products and over-the-counter (OTC) drugs is increasing on a global scale, and studies of phytochemical-OTC drug interactions are becoming more significant. The intake of dietary plants and herbs rich in phytochemicals may affect drug-metabolizing enzymes (DMEs) and transporters. These effects may lead to alterations in pharmacokinetics and pharmacodynamics of OTC drugs when concomitantly administered. Some phytochemical-drug interactions benefit patients through enhanced efficacy, but many interactions cause adverse effects. This review discusses possible mechanisms of phytochemical-OTC drug interactions mediated by phase I and II DMEs and phase III transporters. In addition, current information is summarized for interactions between phytochemicals derived from fruits, vegetables, and herbs and OTC drugs, and counseling is provided on appropriate and safe use of OTC drugs.

Theoretical Study on Storage and Release of Firefly Luciferin

Among numerous bioluminescent organisms, firefly is the most studied one. Recent experiment proposed that sulfoluciferin (SLH₂ ) may serve as a storage form of luciferin (LH₂ ). In the present article, we employed density functional theory calculation to uncover the mechanism and detailed process of the storage and release reactions. Due to lack of available crystallographic structure of the related enzyme, the calculation was performed on a model system. For the storage reaction, possible amino acid residues were used for imitating the protein environment. For the release reaction, the dielectric constant of 3.0 was employed to simulate the polarity of the protein cavity. The computational results indicated that the reactions from LH₂ to SLH₂ and from SLH₂ to LH₂ are both exergonic, which favor the storage and release processes and coincide with the experimental observation. Basing on experimental and current theoretical study, we supplemented the stages of LH₂ storage and release in the entire bioluminescent cycle of firefly. The current theoretical calculation could inspire the study on LH₂ storage and release of other bioluminescent organisms.

Glacier ice archives nearly 15,000-year-old microbes and phages

BACKGROUND

Glacier ice archives information, including microbiology, that helps reveal paleoclimate histories and predict future climate change. Though glacier-ice microbes are studied using culture or amplicon approaches, more challenging metagenomic approaches, which provide access to functional, genome-resolved information and viruses, are under-utilized, partly due to low biomass and potential contamination.

RESULTS

We expand existing clean sampling procedures using controlled artificial ice-core experiments and adapted previously established low-biomass metagenomic approaches to study glacier-ice viruses. Controlled sampling experiments drastically reduced mock contaminants including bacteria, viruses, and free DNA to background levels. Amplicon sequencing from eight depths of two Tibetan Plateau ice cores revealed common glacier-ice lineages including Janthinobacterium, Polaromonas, Herminiimonas, Flavobacterium, Sphingomonas, and Methylobacterium as the dominant genera, while microbial communities were significantly different between two ice cores, associating with different climate conditions during deposition. Separately, ~355- and ~14,400-year-old ice were subject to viral enrichment and low-input quantitative sequencing, yielding genomic sequences for 33 vOTUs. These were virtually all unique to this study, representing 28 novel genera and not a single species shared with 225 environmentally diverse viromes. Further, 42.4% of the vOTUs were identifiable temperate, which is significantly higher than that in gut, soil, and marine viromes, and indicates that temperate phages are possibly favored in glacier-ice environments before being frozen. In silico host predictions linked 18 vOTUs to co-occurring abundant bacteria (Methylobacterium, Sphingomonas, and Janthinobacterium), indicating that these phages infected ice-abundant bacterial groups before being archived. Functional genome annotation revealed four virus-encoded auxiliary metabolic genes, particularly two motility genes suggest viruses potentially facilitate nutrient acquisition for their hosts. Finally, given their possible importance to methane cycling in ice, we focused on Methylobacterium viruses by contextualizing our ice-observed viruses against 123 viromes and prophages extracted from 131 Methylobacterium genomes, revealing that the archived viruses might originate from soil or plants.

CONCLUSIONS

Together, these efforts further microbial and viral sampling procedures for glacier ice and provide a first window into viral communities and functions in ancient glacier environments. Such methods and datasets can potentially enable researchers to contextualize new discoveries and begin to incorporate glacier-ice microbes and their viruses relative to past and present climate change in geographically diverse regions globally. Video Abstract.

The new PFAS C6O4 and its effects on marine invertebrates: First evidence of transcriptional and microbiota changes in the Manila clam Ruditapes philippinarum

There is growing concern for the wide use ofperfluorooctanoic acid (PFOA) because of its toxic effects on the environment and on human health. A new compound - the so called C6O4 (perfluoro ([5-methoxy-1,3-dioxolan-4-yl]oxy) acetic acid) - was recently introduced as one of the alternative to traditional PFOA, however this was done without any scientific evidence of the effects of C6O4 when dispersed into the environment. Recently, the Regional Agency for the Protection of the Environment of Veneto (Italy) detected high levels of C6O4 in groundwater and in the Po river, increasing the alarm for the potential effects of this chemical into the natural environment. The present study investigates for the first time the effects of C6O4 on the Manila clam Ruditapes philippinarum exposed to environmental realistic concentrations of C6O4 (0.1 µg/L and 1 µg/L) for 7 and 21 days. Furthermore, in order to better understand if C6O4 is a valid and less hazardous alternative to its substitute, microbial and transcriptomic alterations were also investigated in clams exposed to 1 µg/L ofPFOA. Results indicate that C6O4 may cause significant perturbations to the digestive gland microbiota, likely determining the impairment of host physiological homeostasis. Despite chemical analyses suggest a 5 times lower accumulation potential of C604 as compared to PFOA in clam soft tissues, transcriptional analyses reveal several alterations of gene expression profile. A large part of the altered pathways, including immune response, apoptosis regulation, nervous system development, lipid metabolism and cell membrane is the same in C6O4 and PFOA exposed clams. In addition, clams exposed to C6O4 showed dose-dependent responses as well as possible narcotic or neurotoxic effects and reduced activation of genes involved in xenobiotic metabolism. Overall, the present study suggests that the potential risks for marine organism following environmental contamination are not reduced by replacing PFOA with C6O4. In addition, the detection of both C6O4 and PFOA into tissues of clams inhabiting the Lagoon of Venice - where there are no point sources of either compounds - recommends a similar capacity to spread throughout the environment. These results prompt the urgent need to re-evaluate the use of C6O4 as it may represent not only an environmental hazard but also a potential risk for human health.

Fluorometric coupled enzyme assay for N-sulfotransferase activity of N-deacetylase/N-sulfotransferase (NDST)

N-Deacetylase/N-sulfotransferases (NDST) are critical enzymes in heparan sulfate (HS) biosynthesis. Radioactive labeling assays are the preferred methods to determine the N-sulfotransferase activity of NDST. In this study, we developed a fluorometric coupled enzyme assay that is suitable for the study of enzyme kinetics and inhibitory properties of drug candidates derived from a large-scale in silico screening targeting the sulfotransferase moiety of NDST1. The assay measures recombinant mouse NDST1 (mNDST1) sulfotransferase activity by employing its natural substrate adenosine 3'-phophoadenosine-5'-phosphosulfate (PAPS), a bacterial analog of desulphated human HS, Escherichia coli K5 capsular polysaccharide (K5), the fluorogenic substrate 4-methylumbelliferylsulfate, and a double mutant of rat phenol sulfotransferase SULT1A1 K56ER68G. Enzyme kinetic analysis of mNDST1 performed with the coupled assay under steady state conditions at pH 6.8 and 37 °C revealed Km (K5) 34.8 μM, Km (PAPS) 10.7 μM, Vmax (K5) 0.53 ± 0.13 nmol/min/μg enzyme, Vmax (PAPS) 0.69 ± 0.05 nmol/min/μg enzyme, and the specific enzyme activity of 394 pmol/min/μg enzyme. The pH optimum of mNDST1 is pH 8.2. Our data indicate that mNDST1 is specific for K5 substrate. Finally, we showed that the mNDST1 coupled assay can be utilized to assess potential enzyme inhibitors for drug development.

The crystal structure of mouse SULT2A8 reveals the mechanism of 7α-hydroxyl, bile acid sulfation

Bile acids play essential roles in facilitating the intestinal absorption of lipophilic nutrients as well as regulation of glucose, lipid, and energy homeostasis via activation of some receptors. Bile acids are cytotoxic, and consequently their concentrations are tightly controlled. A critical pathway for bile acid elimination and detoxification is sulfation. The pattern of bile acid sulfation differs by species. Sulfation preferentially occurs at the 3α-OH of bile acids in humans, but at the 7α-OH in mice. A recent study identified mouse cytosolic sulfotransferase 2A8 (mSULT2A8) as the major hepatic 7α-hydroxyl bile acid-sulfating enzyme. To elucidate the 7α-OH specific sulfation mechanism of mSULT2A8, instead of 3α-OH specific sulfation in humans, we determined a crystal structure of mSULT2A8 in complex with cholic acid, a major bile acid, and 3'-phosphoadenosine-5'-phosphate, the sulfate donor product. Our study shows that bile acid-binding mode of mSULT2A8 and how the enzyme holds the 7α-OH group of bile acids at the catalytic center, revealing that the mechanism underlying 7α-OH specific sulfation. The structure shows the substrate binds to mSULT2A8 in an orientation perpendicular to that of human 3α-hydroxyl bile acid-sulfotransferase (hSULT2A1). The structure of the complex provides new insight into species different bile acid metabolism.

Effects of Genetic Polymorphisms on the Sulfation of Doxorubicin by Human SULT1C4 Allozymes

Doxorubicin is a chemotherapeutic drug widely utilized in cancer treatment. An enzyme critical to doxorubicin metabolism is the cytosolic sulfotransferase (SULT) SULT1C4. This study investigated the functional impact of SULT1C4 single nucleotide polymorphisms (SNPs) on the sulfation of doxorubicin by SULT1C4 allozymes. A comprehensive database search was performed to identify various SULT1C4 SNPs. Ten nonsynonymous SULT1C4 SNPs were selected, and the corresponding cDNAs, packaged in pGEX-2TK expression vector, were generated via site-directed mutagenesis. Respective SULT1C4 allozymes were bacterially expressed and purified by affinity chromatography. Purified SULT1C4 allozymes, in comparison with the wild-type enzyme, were analyzed for sulfating activities toward doxorubicin and 4-nitrophenol, a prototype substrate. Results obtained showed clearly differential doxorubicin-sulfating activity of SULT1C4 allozymes, implying differential metabolism of doxorubicin through sulfation in individuals with distinct SULT1C4 genotypes.

Structure of mouse cytosolic sulfotransferase SULT2A8 provides insight into sulfonation of 7α-hydroxyl bile acids

Cytosolic sulfotransferases (SULTs) catalyze the transfer of a sulfonate group from the cofactor 3'-phosphoadenosine 5'-phosphosulfate to a hydroxyl (OH) containing substrate and play a critical role in the homeostasis of endogenous compounds, including hormones, neurotransmitters, and bile acids. In human, SULT2A1 sulfonates the 3-OH of bile acids; however, bile acid metabolism in mouse is dependent on a 7α-OH sulfonating SULT2A8 via unknown molecular mechanisms. In this study, the crystal structure of SULT2A8 in complex with adenosine 3',5'-diphosphate and cholic acid was resolved at a resolution of 2.5 Å. Structural comparison with human SULT2A1 reveals different conformations of substrate binding loops. In addition, SULT2A8 possesses a unique substrate binding mode that positions the target 7α-OH of the bile acid close to the catalytic site. Furthermore, mapping of the critical residues by mutagenesis and enzyme activity assays further highlighted the importance of Lys44 and His48 for enzyme catalysis and Glu237 in loop 3 on substrate binding and stabilization. In addition, limited proteolysis and thermal shift assays suggested that the cofactor and substrates have protective roles in stabilizing SULT2A8 protein. Together, the findings unveil the structural basis of bile acid sulfonation targeting 7α-OH and shed light on the functional diversity of bile acid metabolism across species.

Glossary and tutorial of xenobiotic metabolism terms used during small molecule drug discovery and development (IUPAC Technical Report)

This project originated more than 15 years ago with the intent to produce a glossary of drug metabolism terms having definitions especially applicable for use by practicing medicinal chemists. A first-draft version underwent extensive beta-testing that, fortuitously, engaged international audiences in a wide range of disciplines involved in drug discovery and development. It became clear that the inclusion of information to enhance discussions among this mix of participants would be even more valuable. The present version retains a chemical structure theme while expanding tutorial comments that aim to bridge the various perspectives that may arise during interdisciplinary communications about a given term. This glossary is intended to be educational for early stage researchers, as well as useful for investigators at various levels who participate on today’s highly multidisciplinary, collaborative small molecule drug discovery teams.

RORα phosphorylation by casein kinase 1α as glucose signal to regulate estrogen sulfation in human liver cells

Estrogen sulfotransferase (SULT1E1) metabolically inactivates estrogen and SULT1E1 expression is tightly regulated by multiple nuclear receptors. Human fetal, but not adult, livers express appreciable amounts of SULT1E1 protein, which is mimicked in human hepatoma-derived HepG2 cells cultured in high glucose (450 mg/dl) medium. Here, we have investigated this glucose signal that leads to phosphorylation of nuclear receptor RORα (NR1F1) at Ser100 and the transcription mechanism by which phosphorylated RORα transduces this signal to nuclear receptor HNF4α, activating the SULT1E1 promoter. The promoter is repressed by non-phosphorylated RORα which binds a distal enhancer (−943/−922 bp) and interacts with and represses HNF4α-mediated transcription. In response to high glucose, RORα becomes phosphorylated at Ser100 and reverses its repression of HNF4α promoter activation. Moreover, the casein kinase CK1α, which is identified in an enhancer-bound nuclear protein complex, phosphorylates Ser100 in in vitro kinase assays. During these dynamic processes, both RORα and HNF4α remain on the enhancer. Thus, RORα utilizes phosphorylation to integrate HNF4α and transduces the glucose signal to regulate the SULT1E1 gene in HepG2 cells and this phosphorylation-mediated mechanism may also regulate SULT1E1 expressions in the human liver.

Biosynthesis of sulfonamide and sulfamate antibiotics in actinomycete

Sulfonamides and sulfamates are a group of organosulfur compounds that contain the signature sulfamoyl structural motif. These compounds were initially only known as synthetic antibacterial drugs but were later also discovered as natural products. Eight highly potent examples have been isolated from actinomycetes to date, illustrating the large biosynthetic repertoire of this bacterial genus. For the biosynthesis of these compounds, several distinct and unique biosynthetic machineries have been discovered, capable to generate the unique S–N bond. For the creation of novel, second generation natural products by biosynthetic engineering efforts, a detailed understanding of the underlying enzyme machinery toward potent structural motifs is crucial. In this review, we aim to summarize the current state of knowledge on sulfonamide and sulfamate biosynthesis. A detailed discussion for the secondary sulfamate ascamycin, the tertiary sulfonamide sulfadixiamycin A, and the secondary sulfonamide SB-203208 is provided and their bioactivities and mode of actions are discussed.

Enzyme Kinetics of PAPS-Sulfotransferase

The cytosolic sulfotransferase (SULT) enzymes are found in human liver, kidney, intestine, and other tissues. These enzymes catalyze the transfer of the -SO₃ group from 3'-phospho-adenosyl-5'-phosphosulfate (PAPS) to a nucleophilic hydroxyl or amine group in a drug substrate. SULTs are stable as dimers, with a highly conserved dimerization domain near the C-terminus of the protein. Crystal structures have revealed flexible loop regions in the native proteins, one of which, located near the dimerization domain, is thought to form a gate that changes position once PAPS is bound to the PAPS-binding site and modulates substrate access and enzyme properties. There is also evidence that oxidation and reduction of certain cysteine residues reversibly regulate the binding of the substrate and PAPS or PAP to the enzyme thus modulating sulfonation. Because SULT enzymes have two substrates, the drug and PAPS, it is common to report apparent kinetic constants with either the drug or the PAPS varied while the other is kept at a constant concentration. The kinetics of product formation can follow classic Michaelis-Menten kinetics, typically over a narrow range of substrate concentrations. Over a wide range of substrate concentrations, it is common to observe partial or complete substrate inhibition with SULT enzymes. This chapter describes the function, tissue distribution, structural features, and properties of the human SULT enzymes and presents examples of enzyme kinetics with different substrates.

Synthesis and structure-activity relationships of cerebroside analogues as substrates of cerebroside sulphotransferase and discovery of a competitive inhibitor

Metachromatic leukodystrophy (MLD) is a rare genetic disease characterised by a dysfunction of the enzyme arylsulphatase A leading to the lysosomal accumulation of cerebroside sulphate (sulphatide) causing subsequent demyelination in patients. The enzyme galactosylceramide (cerebroside) sulphotransferase (CST) catalyses the transfer of a sulphate group from 3'-phosphoadenosine-5'-phosphosulphate (PAPS) to cerebrosides producing sulphatides. Substrate reduction therapy for arylsulphatase A by inhibition of CST was proposed as a promising therapeutic approach. To identify competitive CST inhibitors, we synthesised and investigated analogues of the substrate galactosylceramide with variations at the anomeric position, the acyl substituent and the carbohydrate moiety, and investigated their structure-activity relationships. While most of the compounds behaved as substrates, α-galactosylceramide 16 was identified as the first competitive CST inhibitor. Compound 16 can serve as a new lead structure for the development of drugs for the treatment of this devastating disease, MLD, for which small molecule therapeutics are currently not available.

Evaluation of a conserved tryptophanyl residue in donor substrate binding and catalysis by a phenol sulfotransferase (SULT1A1)

Structural determinations of members of the sulfotransferase (SULT) family suggest a direct interaction between a conserved tryptophanyl side chain and bound 3'-phosphoadenosine-5'-phosphate (PAP). We have prepared and purified mutants of the bovine SULT1A1, a very conserved homolog to the human SULT1A1, in which tryptophanyl-53 was sequentially trimmed to tyrosine, leucine, and alanine. Differential scanning fluorimetry indicated structural stabilities of the mutant proteins comparable to the wild type SULT1A1; however, less thermal stabilizations by PAP plus pentachlorophenol were observed with the mutants, suggesting weakened ligand binding. Protein fluorescence of the wild type enzyme decreased 6.5% upon binding PAP, whereas no changes occurred with the mutant enzymes. This reveals that W53, or its positional counterpart, has been the source of emission intensity changes used in previous investigations of other SULTs. Fluorescence resonance energy transfer from excited tryptophans to bound 7-hydroxycoumarin, as induced by PAP, indicated weakened binding of ligands to the mutant SULTs. This was also encountered and quantified in initial rate kinetic analyses. Ablation of the PAPS adenine-to-W53 ring interaction, shown by the W53A mutant enzyme, resulted in a 6.4-fold increase in K_PAPS and a 92% decrease in k_cat/K_PAPS. Measured K_PAPS values reveal the W53 indole ring contribution to PAPS binding to be 1.1 kcal/mol (4.6 kJ/mol). These results verify the structurally-inferred role for the π-π stacking interaction between PAP(S) and the conserved tryptophanyl residue in SULT1A1 and other members of the SULT family.

Reaction mechanism catalyzed by the dissimilatory adenosine 5'-phosphosulfate reductase. Adenosine 5'-monophosphate inhibitor and key role of arginine 317 in switching the course of catalysis

The present research is a continuation of our work on dissimilatory reduction pathway of sulfate - involved in biogeochemical sulfur turnover. Adenosine 5'-phosphosulfate reductase (APSR) is the second enzyme in the dissimilatory pathway of the sulfate to sulfide reduction. It reversibly catalyzes formation of the sulfite anion (HSO₃^-) from adenosine 5'-phosphosulfate (APS) - the activated form of sulfate provided by ATP sulfurylase (ATPS). Two electrons required for this redox reaction derive from reduced FAD cofactor, which is suggested to be involved directly in the catalysis by formation of FADH-SO₃^- intermediate. The present work covers quantum-mechanical (QM) studies on APSR reaction performed for eight models of APSR active site. The cluster models were constructed based on two crystal structures (PDB codes: 2FJA and 2FJB), differing in conformation of Arg317 active site residue. The described results indicated the most feasible mechanism of APSR forward reaction, including formation of FADH_N-SO₃^- adduct (with proton on N5 atom of isoalloxazine), tautomerization of FADH_N-SO₃^- to FADH_O-SO₃^- (with proton on CO moiety of isoalloxazine), and its reductive cleavage to oxidized FAD and sulfite anion. The reverse reaction proceeds in the backward direction. It is suggested that it requires two AMP molecules, one acting as a substrate and another as an inhibitor of forward reaction, which forces change of Arg317 conformation from "arginine in" (2FJA) to "arginine out" (2FJB). Important role of Arg317 in switching the course of the APSR catalytic reaction is revealed by changing the direction of thermodynamic driving force. The presented research also shows the importance of the protonation pattern of the reduced FAD cofactor and protein residues within the active site.

The Role of Sulfotransferases in Liver Diseases

The cytosolic sulfotransferases (SULTs) are phase II conjugating enzymes that catalyze the transfer of a sulfonate group from the universal sulfate donor 3'-phosphoadenosine-5'-phosphosulfate to a nucleophilic group of their substrates to generate hydrophilic products. Sulfation has a major effect on the chemical and functional homeostasis of substrate chemicals. SULTs are widely expressed in metabolically active or hormonally responsive tissues, including the liver and many extrahepatic tissues. The expression of SULTs exhibits isoform-, tissue-, sex-, and development-specific regulations. SULTs display a broad range of substrates including xenobiotics and endobiotics. The expression of SULTs has been shown to be transcriptionally regulated by members of the nuclear receptor superfamily, such as the peroxisome proliferator-activated receptors, pregnane X receptor, constitutive androstane receptor, vitamin D receptor, liver X receptors, farnesoid X receptor, retinoid-related orphan receptors, estrogen-related receptors, and hepatocyte nuclear factor 4α These nuclear receptors can be activated by numerous xenobiotics and endobiotics, such as fatty acids, bile acids, and oxysterols, many of which are substrates of SULTs. Due to their metabolism of xenobiotics and endobiotics, SULTs and their regulations are implicated in the pathogenesis of many diseases. This review is aimed to summarize the central role of major SULTs, including the SULT1 and SULT2 subfamilies, in the pathophysiology of liver and liver-related diseases. SIGNIFICANCE STATEMENT: Sulfotransferases (SULTs) are indispensable in the homeostasis of xenobiotics and endobiotics. Knowing SULTs and their regulations are implicated in human diseases, it is hoped that genetic or pharmacological manipulations of the expression and/or activity of SULTs can be used to affect the clinical outcome of diseases.

SULT4A1 Modulates Synaptic Development and Function by Promoting the Formation of PSD-95/NMDAR Complex

Sulfotransferase 4A1 (SULT4A1) is a cytosolic sulfotransferase that is highly conserved across species and extensively expressed in the brain. However, the biological function of SULT4A1 is unclear. SULT4A1 has been implicated in several neuropsychiatric disorders, such as Phelan-McDermid syndrome and schizophrenia. Here, we investigate the role of SULT4A1 within neuron development and function. Our data demonstrate that SULT4A1 modulates neuronal branching complexity and dendritic spines formation. Moreover, we show that SULT4A1, by negatively regulating the catalytic activity of Pin1 toward PSD-95, facilitates NMDAR synaptic expression and function. Finally, we demonstrate that the pharmacological inhibition of Pin1 reverses the pathologic phenotypes of neurons knocked down by SULT4A1 by specifically restoring dendritic spine density and rescuing NMDAR-mediated synaptic transmission. Together, these findings identify SULT4A1 as a novel player in neuron development and function by modulating dendritic morphology and synaptic activity.SIGNIFICANCE STATEMENT Sulfotransferase 4A1 (SULT4A1) is a brain-specific sulfotransferase highly expressed in neurons. Different evidence has suggested that SULT4A1 has an important role in neuronal function and that SULT4A1 altered expression might represent a contributing factor in multiple neurodevelopmental disorders. However, the function of SULT4A1 in the mammalian brain is still unclear. Here, we demonstrate that SULT4A1 is highly expressed at postsynaptic sites where it sequesters Pin1, preventing its negative action on synaptic transmission. This study reveals a novel role of SULT4A1 in the modulation of NMDA receptor activity and strongly contributes to explaining the neuronal dysfunction observed in patients carrying deletions of SULTA41 gene.

Why does oxamniquine kill Schistosoma mansoni and not S. haematobium and S. japonicum?

Human schistosomiasis is a disease which globally affects over 229 million people. Three major species affecting humans are Schistosoma mansoni, S. haematobium and S. japonicum. Previous treatment of S. mansoni includes the use of oxamniquine (OXA), a prodrug that is enzymatically activated in S. mansoni but is ineffective against S. haematobium and S. japonicum. The OXA activating enzyme was identified and crystallized, as being a S. mansoni sulfotransferase (SmSULT). S. haematobium and S. japonicum possess homologs of SmSULT (ShSULT and SjSULT) begging the question; why does oxamniquine fail to kill S. haematobium and S. japonicum adult worms? Investigation of the molecular structures of the sulfotransferases indicates that structural differences, specifically in OXA contact residues, do not abrogate OXA binding in the active sites as previously hypothesized. Data presented argue that the ability of SULTs to sulfate and thus activate OXA and its derivatives is linked to the ability of OXA to fit in the binding pocket to allow the transfer of a sulfur group.

Selectins-The Two Dr. Jekyll and Mr. Hyde Faces of Adhesion Molecules-A Review

Selectins belong to a group of adhesion molecules that fulfill an essential role in immune and inflammatory responses and tissue healing. Selectins are glycoproteins that decode the information carried by glycan structures, and non-covalent interactions of selectins with these glycan structures mediate biological processes. The sialylated and fucosylated tetrasaccharide sLe^x is an essential glycan recognized by selectins. Several glycosyltransferases are responsible for the biosynthesis of the sLe^x tetrasaccharide. Selectins are involved in a sequence of interactions of circulated leukocytes with endothelial cells in the blood called the adhesion cascade. Recently, it has become evident that cancer cells utilize a similar adhesion cascade to promote metastases. However, like Dr. Jekyll and Mr. Hyde’s two faces, selectins also contribute to tissue destruction during some infections and inflammatory diseases. The most prominent function of selectins is associated with the initial stage of the leukocyte adhesion cascade, in which selectin binding enables tethering and rolling. The first adhesive event occurs through specific non-covalent interactions between selectins and their ligands, with glycans functioning as an interface between leukocytes or cancer cells and the endothelium. Targeting these interactions remains a principal strategy aimed at developing new therapies for the treatment of immune and inflammatory disorders and cancer. In this review, we will survey the significant contributions to and the current status of the understanding of the structure of selectins and the role of selectins in various biological processes. The potential of selectins and their ligands as therapeutic targets in chronic and acute inflammatory diseases and cancer will also be discussed. We will emphasize the structural characteristic of selectins and the catalytic mechanisms of glycosyltransferases involved in the biosynthesis of glycan recognition determinants. Furthermore, recent achievements in the synthesis of selectin inhibitors will be reviewed with a focus on the various strategies used for the development of glycosyltransferase inhibitors, including substrate analog inhibitors and transition state analog inhibitors, which are based on knowledge of the catalytic mechanism.

Mechanistic Insights into the Effect of Ligands on Structural Stability and Selectivity of Sulfotransferase 2A1 (SULT2A1)

Cytosolic sulfotransferases (SULTs) acting as phase II metabolic enzymes can be used in the sulfonation of small molecules by transferring a sulfonate group from the unique co-factor 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to the substrates. In the present study, molecular dynamics (MD) simulations and ensemble docking study were employed to theoretically characterize the mechanism for the effect of co-factor (PAP) and ligands (LCA, raloxifene, α-hydroxytamoxifen, ouabain, and 3'-phosphoadenylyl sulfate) on structural stability and selectivity of SULT2A1 from the perspective of the dynamic behavior of SULT2A1 structures. Structural stability and network analyses indicated that the cooperation between PAP and LCA may enhance the thermal stability and compact communication in enzymes. During the MD simulations, the obviously rigid region and inward displacement were detected in the active-site cap (loop16) of the conformation containing PAP, which may be responsible for the significant changes in substrate accessibility and catalytic activity. The smaller substrates such as LCA could bind stably to the active pocket in the presence of PAP. However, the substrates or inhibitors with a large spatial structure needed to bind to the open conformation (without PAP) prior to PAPS binding.

A comparative study of 3 alternative avian toxicity testing methods: Effects on hepatic gene expression in the chicken embryo

There is growing interest in developing alternative methods to screen and prioritize chemical hazards, although few studies have compared responses across different methods. The objective of the present study was to compare 3 alternative liver methods derived from white Leghorn chicken (Gallus gallus domesticus): primary hepatocyte culture, liver slices, and liver from in ovo injected embryos. We examined hepatic gene expression changes after exposure to 3 chemicals (17β-trenbolone [17βT], 17β-estradiol [E2], and 2,3,7,8-tetrachlorodibenzo-p-dioxin [TCDD]) using a custom quantitative polymerase chain reaction (qPCR) array with 7 genes (vitellogenin [VTG], apolipoprotein [Apo], cytochrome P450 1A4 [CYP1A4], liver basic fatty acid binding protein [LBFABP], 3β hydroxysteroid dehydrogenase [HSD3β1], stearoyl coenzyme A desaturase [SCD], and estrogen sulfotransferase [SULT1E1]). Gene expression across the 3 methods was examined using hierarchical clustering. Up-regulation of CYP1A4 in response to TCDD was consistent across all methods, and the magnitude was higher in hepatocytes (>150-fold) compared with slices (>31-fold) and in ovo liver (>27-fold). In hepatocytes, SCD and VTG up-regulation in response to 17βT and E2 was >4-fold and 16-fold, respectively. The rank order of cases with significant changes in gene expression among the 3 methods was: hepatocytes (22) > in ovo liver (11) > liver slices (6). Hierarchical clustering grouped liver slices and in ovo liver as more similar, whereas hepatocytes were grouped separately from in ovo liver. More introspective comparisons are needed to understand how and why alternative methods differ and to aid in their integration into toxicity testing. Environ Toxicol Chem 2019;38:2546-2555. © 2019 SETAC.