Per- and polyfluoroalkyl substances inhibit human and rat 17ß-hydroxysteroid dehydrogenase 1: Quantitative structure-activity relationship and molecular docking analysis.

Per- and polyfluoroalkyl (PFAS) substances are enduring industrial materials. 17ß-Hydroxysteroid dehydrogenase isoform 1 (17ß-HSD1) is an estrogen metabolizing enzyme, which transforms estrone into estradiol in human placenta and rat ovary. Whether PFAS inhibit 17ß-HSD1 and what the structure-activity relationship (SAR) remains unexplored. We screened 18 PFAS for inhibiting human and rat 17ß-HSD1 in microsomes and studied their SAR and mode of action(MOA). Of the 11 perfluorocarboxylic acids (PFCAs), C8-C14 PFCAs at a concentration of 100 µM substantially inhibited human 17ß-HSD1, with order of C11 (half-maximal inhibition concentration, IC50, 8.94 µM) > C10 (10.52 µM) > C12 (14.90 µM) > C13 (30.97 µM) > C9 (43.20 µM) > C14 (44.83 µM) > C8 (73.38 µM) > others. Of the 7 per- and poly-fluorosulfonic acids (PFSAs), the potency was C8S (IC50, 14.93 µM) > C7S (80.70 µM) > C6S (177.80 µM) > others. Of the PFCAs, C8-C14 PFCAs at 100 µM markedly reduced rat 17ß-HSD1 activity, with order of C11 (IC50, 9.11 µM) > C12 (14.30 µM) > C10 (18.24 µM) > C13 (25.61 µM) > C9 (67.96 µM) > C8 (204.39 µM) > others. Of the PFSAs, the potency was C8S (IC50, 37.19 µM) > C7S (49.38 µM) > others. In contrast to PFOS (C6S), the partially fluorinated compound 6:2 FTS with an equivalent number of carbon atoms demonstrated no inhibition of human and rat 17ß-HSD1 activity at a concentration of 100 µM. The inhibition of human and rat enzymes by PFAS followed a V-shaped trend from C4 to C14, with a nadir at C11. Moreover, human 17ß-HSD1 was more sensitive than rat enzyme. PFAS inhibited human and rat 17ß-HSD1 in a mixed mode. Docking analysis revealed that they bind to the NADPH and steroid binding site of both 17ß-HSD1 enzymes. The 3D quantitative SAR (3D-QSAR) showed that hydrophobic region, hydrogen bond acceptor and donor are key factors in binding to 17ß-HSD1 active sites. In conclusion, PFAS exhibit inhibitory effects on human and rat 17ß-HSD1 depending on factors such as carbon chain length, degree of fluorination, and the presence of carboxylic acid or sulfonic acid groups, with a notable V-shaped shift observed at C11.

Structural basis of lipid-droplet localization of 17-beta-hydroxysteroid dehydrogenase 13.

Hydroxysteroid 17-beta-dehydrogenase 13 (HSD17B13) is a hepatic lipid droplet-associated enzyme that is upregulated in patients with non-alcoholic fatty liver disease. Recently, there have been several reports that predicted loss of function variants in HSD17B13 protect against the progression of steatosis to non-alcoholic steatohepatitis with fibrosis and hepatocellular carcinoma. Here we report crystal structures of full length HSD17B13 in complex with its NAD+ cofactor, and with lipid/detergent molecules and small molecule inhibitors from two distinct series in the ligand binding pocket. These structures provide insights into a mechanism for lipid droplet-associated proteins anchoring to membranes as well as a basis for HSD17B13 variants disrupting function. Two series of inhibitors interact with the active site residues and the bound cofactor similarly, yet they occupy different paths leading to the active site. These structures provide ideas for structure-based design of inhibitors that may be used in the treatment of liver disease.

Lessons from 17ß-HSD3 deficiency: Clinical spectrum and complex molecular basis in Chinese patients.

17ß-Hydroxysteroid dehydrogenase type 3 (17ß-HSD3) deficiency is rarely reported in Chinese patients with 46, XY disorders of sexual development (DSD). Seven subjects with 17ß-HSD3 deficiency were identified from 206 Chinese 46, XY DSD patients using targeted next-generation sequencing (NGS). Serum AD and T levels were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS). In silico and functional studies were performed to evaluate the enzymatic activity impairment of HSD17B3 variants. A minigene assay was performed in an exonic splicing variant. Our results showed that four novel and five reported HSD17B3 variants were identified in 7 unrelated patients. The patients showed cryptic presentation during childhood and classical virilization after puberty with T/AD ratio< 0.4. A heterozygous large deletion from the 5'UTR to exon 1 was identified in a patient with a monoallelic variant of p.N130S. Although predicted to be 'likely pathogenic', only p. S232P and p. S160F drastically reduced the enzymatic activity of 17ß-HSD3. A previously reported 'missense' variant c 0.277 G>A (p. E93K) was revealed to have no impact on enzyme activity but resulted in aberrant splicing of exon 3 and was reclassified as an exonic splicing variant. In our study, one nonsense, one exonic splicing, one deletion, one large deletion and five missense variants were detected in patients with 17ß-HSD3 deficiency, expanding the clinical and molecular profile of this disorder. In silico analysis should be cautiously interpreted when the heredity pattern and functional study are inconsistent.

Substituted Aryl Benzylamines as Potent and Selective Inhibitors of 17ß-Hydroxysteroid Dehydrogenase Type 3.

17ß-Hydroxysteroid dehydrogenase type 3 (17ß-HSD3) is expressed at high levels in testes and seminal vesicles; it is also present in prostate tissue and involved in gonadal and non-gonadal testosterone biosynthesis. The enzyme is membrane-bound, and a crystal structure is not yet available. Selective aryl benzylamine-based inhibitors were designed and synthesised as potential agents for prostate cancer therapeutics through structure-based design, using a previously built homology model with docking studies. Potent, selective, low nanomolar IC50 17ß-HSD3 inhibitors were discovered using N-(2-([2-(4-chlorophenoxy)phenylamino]methyl)phenyl)acetamide (1). The most potent compounds have IC50 values of approximately 75 nM. Compound 29, N-[2-(1-Acetylpiperidin-4-ylamino)benzyl]-N-[2-(4-chlorophenoxy)phenyl]acetamide, has an IC50 of 76 nM, while compound 30, N-(2-(1-[2-(4-chlorophenoxy)-phenylamino]ethyl)phenyl)acetamide, has an IC50 of 74 nM. Racemic C-allyl derivative 26 (IC50 of 520 nM) was easily formed from 1 in good yield and, to determine binding directionality, its enantiomers were separated by chiral chromatography. Absolute configuration was determined using single crystal X-ray crystallography. Only the S-(+)-enantiomer (32) was active with an IC50 of 370 nM. Binding directionality was predictable through our in silico docking studies, giving confidence to our model. Importantly, all novel inhibitors are selective over the type 2 isozyme of 17ß-HSD2 and show <20% inhibition when tested at 10 µM. Lead compounds from this series are worthy of further optimisation and development as inhibitors of testosterone production by 17ß-HSD3 and as inhibitors of prostate cancer cell growth.

Rational design of 17ß-hydroxysteroid dehydrogenase type3 for improving testosterone production with an engineered Pichia pastoris.

Testosterone (TS) is a critical androgenic steroid that regulates human metabolism and maintains secondary sexual characteristics. The biotransformation from 4-androstene-3,17-done (4-AD) to TS is limited by the poor catalytic activity of 17ß-hydroxysteroid dehydrogenase type 3 (17ß-HSD3). Herein, we explored the structural characteristics and catalytic mechanism of 17ß-HSD3 and adopted the rational design strategy to improve its catalytic activity. Molecular docking and molecular dynamics simulations revealed the substrate-binding pocket and the binding mode of 4-AD to 17ß-HSD3. We located the pivotal residues and regulated their hydrophobicity and polarity. The obtained G186R/Y195W variant formed additional electrostatic interaction and hydrogen bond with 4-AD, increasing the binding affinity between the variant and 4-AD. Therefore, the G186R/Y195W variant produced 3.98 g/L of TS, which increased to 297%. The combination of structural and mechanism resolution drives the implementation of the rational design strategy, which provides guidance for bioproduction of TS catalyzed by 17ß-HSD3.

16-Picolyl-androsterone derivative exhibits potent 17ß-HSD3 inhibitory activity, improved metabolic stability and cytotoxic effect on various cancer cells: Synthesis, homology modeling and docking studies.

A new androsterone derivative bearing a 16ß-picolyl group (compound 5; FCO-586-119) was synthetized in four steps from the lead compound 1 (RM-532-105). We measured its inhibitory activity on 17ß-HSD3 using microsomal fraction of rat testes as well as transfected LNCaP[17ß-HSD3] cells. We then assessed its metabolic stability as well as its cytotoxic effect against a panel of cancer cell lines. The addition of a picolyl moiety at C-16 of RM-532-105 steroid core improves the 17ß-HSD3 inhibitory activity in the microsomal fraction of rat testes, but not in whole LNCaP[17ß-HSD3] cells. Interestingly, this structural modification enhances 3-fold the metabolic stability in conjunction with a significant cytotoxic effect against pancreatic, ovarian, breast, lung, and prostate cancer cells. Because the inhibitory activity data against 17ß-HSD3 suggested that both steroid derivatives are non-competitive inhibitors, we performed docking and molecular dynamics simulations using a homology model of this membrane-associated enzyme. The results of these simulations revealed that both RM-532-105 (1) and FCO-586-119 (5) can compete for the cofactor-binding site displaying better binding energy than NADP+.

Study of Biomolecular Interactions of Mitochondrial Proteins Related to Alzheimer's Disease: Toward Multi-Interaction Biomolecular Processes.

Progressive mitochondrial dysfunction due to the accumulation of amyloid beta (Aß) peptide within the mitochondrial matrix represents one of the key characteristics of Alzheimer's disease (AD) and appears already in its early stages. Inside the mitochondria, Aß interacts with a number of biomolecules, including cyclophilin D (cypD) and 17ß-hydroxysteroid dehydrogenase type 10 (17ß-HSD10), and affects their physiological functions. However, despite intensive ongoing research, the exact mechanisms through which Aß impairs mitochondrial functions remain to be explained. In this work, we studied the interactions of Aß with cypD and 17ß-HSD10 in vitro using the surface plasmon resonance (SPR) method and determined the kinetic parameters (association and dissociation rates) of these interactions. This is the first work which determines all these parameters under the same conditions, thus, enabling direct comparison of relative affinities of Aß to its mitochondrial binding partners. Moreover, we used the determined characteristics of the individual interactions to simulate the concurrent interactions of Aß with cypD and 17ß-HSD10 in different model situations associated with the progression of AD. This study not only advances the understanding of Aß-induced processes in mitochondria during AD, but it also provides a new perspective on research into complex multi-interaction biomolecular processes in general.

A Hybrid In Silico/In Vitro Target Fishing Study to Mine Novel Targets of Urolithin A and B: A Step Towards a Better Comprehension of Their Estrogenicity.

SCOPE: Urolithin A and B are gut metabolites of ellagic acid and ellagitannins associated with many beneficial effects. Evidence in vitro pointed to their potential as estrogenic modulators. However, both molecular mechanisms and biological targets involved in such activity are still poorly characterized, preventing a comprehensive understanding of their bioactivity in living organisms. This study aimed at rationally identifying novel biological targets underlying the estrogenic-modulatory activity of urolithins. METHODS AND RESULTS: The work relies on an in silico/in vitro target fishing study coupling molecular modeling with biochemical and cell-based assays. Estrogen sulfotransferase and 17ß-hydroxysteroid dehydrogenase are identified as potentially subject to inhibition by the investigated urolithins. The inhibition of the latter undergoes experimental confirmation either in a cell-free or cell-based assay, validating computational outcomes. CONCLUSIONS: The work describes target fishing as an effective tool to identify unexpected targets of food bioactives detailing the interaction at a molecular level. Specifically, it described, for the first time, 17ß-hydroxysteroid dehydrogenase as a target of urolithins and highlighted the need of further investigations to widen the understanding of urolithins as estrogen modulators in living organisms.

Human dehydrogenase/reductase SDR family member 11 (DHRS11) and aldo-keto reductase 1C isoforms in comparison: Substrate and reaction specificity in the reduction of 11-keto-C19-steroids.

Recent studies have shown that an adrenal steroid 11ß-hydroxy-4-androstene-3,17-dione serves as the precursor to androgens, 11-ketotestosterone and 11-ketodihydrotestosterone (11KDHT). The biosynthetic pathways include the reduction of 3- and 17-keto groups of the androgen precursors 11-keto-C19-steroids, which has been reported to be mediated by three human enzymes; aldo-keto reductase (AKR)1C2, AKR1C3 and 17ß-hydroxysteroid dehydrogenase (HSD) type-3. To explore the contribution of the enzymes in the reductive metabolism, we kinetically compared the substrate specificity for 11-keto-C19-steroids among purified recombinant preparations of four AKRs (1C1, 1C2,1C3 and 1C4) and DHRS11, which shows 17ß-HSD activity. Although AKR1C1 did not reduce the 11-keto-C19-steroids, AKR1C3 and DHRS11 reduced 17-keto groups of 11-keto-4-androstene-3,17-dione, 11-keto-5α-androstane-3,17-dione (11K-Adione) and 11-ketoandrosterone with Km values of 5-28 µM. The 3-keto groups of 11KDHT and 11K-Adione were reduced by AKR1C4 (Km 1 µM) more efficiently than by AKR1C2 (Km 5 and 8 µM, respectively). GC/MS analysis of the products showed that DHRS11 acts as 17ß-HSD, and that AKR1C2 and AKR1C4 are predominantly 3α-HSDs, but formed a minor 3ß-metabolite from 11KDHT. Since DHRS11 was thus newly identified as 11-keto-C19-steroid reductase, we also investigated its substrate-binding mode by molecular docking and site-directed mutagenesis of Thr163 and Val200, and found the following structural features: 1). There is a space that accommodates the 11-keto group of the 11-keto-C19-steroids in the substrate-binding site. 2) Val200 is a critical determinant for exhibiting the strict 17ß-HSD activity of the enzyme, because the Val200Leu mutation resulted in both significant impairment of the 17ß-HSD activity and emergence of 3ß-HSD activity towards 5α-androstanes including 11KDHT.

Characteristics and sex dimorphism of 17ß-hydroxysteroid dehydrogenase family genes in the olive flounder Paralichthys olivaceus.

Sex steroid hormones play important roles in fish sex differentiation, gonadal development and secondary sexual characteristics. Olive flounder Paralichthys olivaceus is a valuable commercial marine fish species and has marked sexual dimorphism. However, the mechanisms of action of sex hormones in flounder sex are still unclear. In this study, a total of ten Hsd17b family genes, including Hsd17b3, -4, -7, -8, -9, -10, -12a, -12b, -14 and -15, were identified in the flounder, which encoded critical enzymes acting on sex steroid synthesis and metabolism. Hsd17b genes were distributed on eight chromosomes. Hsd17b12a and -12b were located on chromosomes 19 and 7, respectively. It was speculated that these two genes were just highly similar rather than different transcripts derived from the same gene. According to the results of domain and motif analyses, they all belonged to the SDR superfamily and contained conserved Hsd17b motifs TGxxxGxG, PGxxxT, NNAG and YxxxK. Analysis of amino acid sequences predicted that Hsd17b1, -4, -7, -12a and -14 were hydrophilic proteins. The stability of Hsd17b1, -3 and -12b proteins was predicted to be low. The various Hsd17b family genes differed in tissue expression pattern, and Hsd17b10, -12a and -12b were highly expressed in the flounder ovary. Moreover, throughout gonadal development, Hsd17b3 was highly expressed in the testis, and Hsd17b1, -12a and -12b were highly expressed in the ovary, suggesting that they might play an important role in testosterone synthesis in the testis or estrogen synthesis in the ovary. Activities of Hsd17b3 at stages I-V were all significantly higher in the testis than in the ovary (P < 0.05, P < 0.01). Transfection analysis in HEK293T cells showed that Hsd17b1 and -3 were located in both the cytoplasm and nucleus. Additionally, after challenging fish with tamoxifen, Hsd17b3 expression level in the testis decreased significantly (P < 0.01), and in the ovary no significant change was observed. Moreover, the expression of Hsd17b1 in the ovary was significantly upregulated after injection with flutamide (P < 0.05). These findings introduce the characteristics of the flounder Hsd17b in subfamily, which contribute to our understanding of the regulation of sex steroid hormone synthesis in fish gonadal development.

Ionic Environment Affects Biomolecular Interactions of Amyloid-ß: SPR Biosensor Study.

In early stages of Alzheimer's disease (AD), amyloid beta (Aß) accumulates in the mitochondrial matrix and interacts with mitochondrial proteins, such as cyclophilin D (cypD) and 17ß-hydroxysteroid dehydrogenase 10 (17ß-HSD10). Multiple processes associated with AD such as increased production or oligomerization of Aß affect these interactions and disbalance the equilibrium between the biomolecules, which contributes to mitochondrial dysfunction. Here, we investigate the effect of the ionic environment on the interactions of Aß (Aß1-40, Aß1-42) with cypD and 17ß-HSD10 using a surface plasmon resonance (SPR) biosensor. We show that changes in concentrations of K+ and Mg2+ significantly affect the interactions and may increase the binding efficiency between the biomolecules by up to 35% and 65% for the interactions with Aß1-40 and Aß1-42, respectively, in comparison with the physiological state. We also demonstrate that while the binding of Aß1-40 to cypD and 17ß-HSD10 takes place preferentially around the physiological concentrations of ions, decreased concentrations of K+ and increased concentrations of Mg2+ promote the interaction of both mitochondrial proteins with Aß1-42. These results suggest that the ionic environment represents an important factor that should be considered in the investigation of biomolecular interactions taking place in the mitochondrial matrix under physiological as well as AD-associated conditions.

Novel Benzothiazole-based Ureas as 17ß-HSD10 Inhibitors, A Potential Alzheimer's Disease Treatment.

: It has long been established that mitochondrial dysfunction in Alzheimer's disease (AD) patients can trigger pathological changes in cell metabolism by altering metabolic enzymes such as the mitochondrial 17ß-hydroxysteroid dehydrogenase type 10 (17ß-HSD10), also known as amyloid-binding alcohol dehydrogenase (ABAD). We and others have shown that frentizole and riluzole derivatives can inhibit 17ß-HSD10 and that this inhibition is beneficial and holds therapeutic merit for the treatment of AD. Here we evaluate several novel series based on benzothiazolylurea scaffold evaluating key structural and activity relationships required for the inhibition of 17ß-HSD10. Results show that the most promising of these compounds have markedly increased potency on our previously published inhibitors, with the most promising exhibiting advantageous features like low cytotoxicity and target engagement in living cells.

A- and D-Ring Structural Modifications of an Androsterone Derivative Inhibiting 17ß-Hydroxysteroid Dehydrogenase Type 3: Chemical Synthesis and Structure-Activity Relationships.

Decreasing the intratumoral androgen biosynthesis by using an inhibitor of 17ß-hydroxysteroid dehydrogenase type 3 (17ß-HSD3) is a strategy to treat prostate cancer. The androsterone (ADT) derivative 1 (RM-532-105) has shown strong inhibitory activity on 17ß-HSD3, but needs to be improved. Herein, we describe the chemical synthesis and characterization of two series of analogues to address the impact of A- and D-ring modifications on 17ß-HSD3 inhibitory activity, androgenic effect, and metabolic stability. Structure-activity relationships were generated by adding different groups at C16/C17 (D-ring diversification) or replacing the ADT backbone by a nor-androstane or an estrane backbone (A-ring diversification). D-ring derivatives were less potent inhibitors than lead compound 1, whereas steroidal backbone (A-ring) change led to identifying promising novel estrane derivatives. This culminated with potent 17ß-HSD3 inhibitors 23, 27, 31, and 33 (IC50 = 0.10, 0.02, 0.13, and 0.17 µM, respectively), which did not stimulate LAPC-4 cell proliferation and displayed higher plasma concentration in mice than lead compound 1.

A SNP in a Steroidogenic Enzyme Is Associated with Phenotypic Sex in Seriola Fishes.

Vertebrate sex development consists largely of two processes: "sex determination," the initial bifurcation of sexual identity, and "sex differentiation," which subsequently facilitates maleness or femaleness according to the sex determination signal. Steroid hormones promote multiple types of sexual dimorphism in eutherian mammals and avians [1-3], in which they are indispensable for proper sex differentiation. By contrast, in many poikilothermic vertebrates, steroid hormones have been proposed to be key players in sex determination as well as sex differentiation [4-8]. This hypothesis was introduced more than 50 years ago but has never been rigorously tested due to difficulties in discriminating the roles of steroids in sex determination and differentiation. We found that a missense SNP in the gene encoding the steroidogenic enzyme 17ß-hydroxysteroid dehydrogenase 1 (Hsd17b1) was perfectly associated with ZZ/ZW sex determination in Seriola fishes. Biochemical analyses revealed that a glutamate residue present specifically in Z-type HSD17B1 attenuated interconversion between 17-keto and 17ß-hydroxy steroids relative to the allelic product from the W chromosome, which harbors glycine at that position, by disrupting the hydrogen bond network between the steroid and the enzyme's catalytic residues. Hsd17b1 mRNA is constitutively expressed in undifferentiated and differentiating gonads of both genotypic sexes, whereas W-type mRNA is expressed only in genotypic females. Meanwhile, Cyp19a1 is predominantly expressed in differentiating ovary. We conclude that the combination of Hsd17b1 alleles determines sex by modulating endogenous estrogen levels in Seriola species. These findings strongly support the long-standing hypothesis on steroids in sex determination.

Mutational and structural studies uncover crucial amino acids determining activity and stability of 17ß-HSD14.

17ß-Hydroxysteroid dehydrogenase type 14 (17ß-HSD14) catalyzes the conversion of highly active estrogens and androgens into their less active oxidized forms in presence of NAD+ as cofactor. The crystal structure of 17ß-HSD14 has been determined, however, the role of individual amino acids likely involved in the enzymatic function remains poorly understood. Objective of this study was to further characterize the enzyme by site-directed mutagenesis considering five amino acids next to the catalytic center. The tools used for the characterization of the enzyme variants are X-ray crystallography and enzyme kinetics. Lys158 was confirmed to belong to the catalytic triad. Tyr253', located on the C-terminal loop of the adjacent monomer, enters into the active site of the neighboring monomer and interacts with the catalytic Tyr154. Therefore, Tyr253' helps to tie the two monomers together. Cys255, located at the interface between both monomers, can form a disulfide bridge with the Cys255' from the adjacent monomer. In contrast to the contact provided by Tyr253, the latter interaction is not crucial for dimer formation. His93 and Gln148 are located at the rim of the substrate binding pocket. His93 does not interact directly with the ligand in the active site. However, it influences the turnover of the enzyme. The Gln148 restricts in size the access tunnel of the substrate to the binding pocket.

Subcellular localization and membrane topology of 17ß-hydroxysteroid dehydrogenases.

The 17ß-hydroxysteroid dehydrogenases (17ß-HSDs) comprise enzymes initially identified by their ability to interconvert active and inactive forms of sex steroids, a vital process for the tissue-specific control of estrogen and androgen balance. However, most 17ß-HSDs have now been shown to accept substrates other than sex steroids, including bile acids, retinoids and fatty acids, thereby playing unanticipated roles in cell physiology. This functional divergence is often reflected by their different subcellular localization, with 17ß-HSDs found in the cytosol, peroxisome, mitochondria, endoplasmic reticulum and in lipid droplets. Moreover, a subset of 17ß-HSDs are integral membrane proteins, with their specific topology dictating the cellular compartment in which they exert their enzymatic activity. Here, we summarize the present knowledge on the subcellular localization and membrane topology of the 17ß-HSD enzymes and discuss the correlation with their biological functions.

Crystal structures of human 17ß-hydroxysteroid dehydrogenase type 1 complexed with estrone and NADP+ reveal the mechanism of substrate inhibition.

Human 17ß-hydroxysteroid dehydrogenase type 1 (17ß-HSD1) catalyses the last step in estrogen activation and is thus involved in estrogen-dependent diseases (EDDs). Unlike other 17ß-HSD members, 17ß-HSD1 undergoes a significant substrate-induced inhibition that we have previously reported. Here we solved the binary and ternary crystal structures of 17ß-HSD1 in complex with estrone (E1) and cofactor analog NADP+ , demonstrating critical enzyme-substrate-cofactor interactions. These complexes revealed a reversely bound E1 in 17ß-HSD1 that provides the basis of the substrate inhibition, never demonstrated in estradiol complexes. Structural analysis showed that His221 is the key residue responsible for the reorganization and stabilization of the reversely bound E1, leading to the formation of a dead-end complex, which exists widely in NADP(H)-preferred enzymes for the regulation of their enzymatic activity. Further, a new inhibitor is proposed that may inhibit 17ß-HSD1 through the formation of a dead-end complex. This finding indicates a simple mechanism of enzyme regulation in the physiological background and introduces a pioneer inhibitor of 17ß-HSD1 based on the dead-end inhibition model for efficiently targeting EDDs. DATABASES: Coordinates and structure factors of 17ß-HSD1-E1 and 17ß-HSD1-E1-NADP+ have been deposited in the Protein Data Bank with accession code 6MNC and 6MNE respectively. ENZYMES: 17ß-hydroxysteroid dehydrogenase type 1 (17ß-HSD1) EC 1.1.1.62.

17B-hydroxysteroid dehydrogenases as acyl thioester metabolizing enzymes.

17ß-Hydroxysteroid dehydrogenases (HSD17B) catalyze the oxidation/reduction of 17ß-hydroxy/keto group in position C17 in C18- and C19 steroids. Most HSD17Bs are also catalytically active with substrates other than steroids. A subset of these enzymes is able to process thioesters of carboxylic acids. This group of enzymes includes HSD17B4, HSD17B8, HSD17B10 and HSD17B12, which execute reactions in intermediary metabolism, participating in peroxisomal ß-oxidation of fatty acids, mitochondrial oxidation of 3R-hydroxyacyl-groups, breakdown of isoleucine and fatty acid chain elongation in endoplasmic reticulum. Divergent substrate acceptance capabilities exemplify acquirement of catalytic site adaptiveness during evolution. As an additional common feature these HSD17Bs are multifunctional enzymes that arose either via gene fusions (HSD17B4) or are incorporated as subunits into multifunctional protein complexes (HSD17B8 and HSD17B10). Crystal structures of HSD17B4, HSD17B8 and HSD17B10 give insight into their structure-function relationships. Thus far, deficiencies of HSD17B4 and HSD17B10 have been assigned to inborn errors in humans, underlining their significance as enzymes of metabolism.

Role of HSD17B13 in the liver physiology and pathophysiology.

17ß-Hydroxysteroid dehydrogenases (HSD17Bs) comprise a large family of 15 members that are mainly involved in sex hormone metabolism. Some HSD17Bs enzymes also play key roles in cholesterol and fatty acid metabolism. Recent study showed that hydroxysteroid 17ß-dehydrogenase 13 (HSD17B13), an enzyme with unknown biological function, is a novel liver-specific lipid droplet (LD)-associated protein in mouse and humans. HSD17B13 expression is markedly upregulated in patients and mice with non-alcoholic fatty liver disease (NAFLD). Hepatic overexpression of HSD17B13 promotes lipid accumulation in the liver. In this review, we summarize recent progress regarding the role of HSD17B13 in the regulation of hepatic lipid homeostasis and discuss genetic, genomic and proteomic evidence supporting the pathogenic role of HSD17B13 in NAFLD. We also emphasize its potential as a biomarker of advanced liver disease, such as non-alcoholic steatohepatitis (NASH) and liver cancer.