Structure and inhibition mechanism of the catalytic domain of human squalene epoxidase

Structural Basis of Sequential Enantioselective Epoxidation by a Flavin-Dependent Monooxygenase in Lasalocid A Biosynthesis

Polyether polyketides are a structurally diverse group of natural products known for their antimicrobial and antiproliferative activities. Lasalocid A is a canonical natural polyether produced by the soil bacterium Streptomyces lasalocidi. In lasalocid A biosynthesis, a polyene polyketide intermediate is converted into a bisepoxide by the flavin-dependent monooxygenase enzyme Lsd18. Remarkably, Lsd18 acts on two distinct C═C groups in the substrate molecule, forming two (R,R) epoxides. We have determined the X-ray crystal structures of Lsd18 in the substrate-free, substrate-bound, and product-bound forms. Our work has revealed that Lsd18 has an extra-large substrate-binding pocket that allows the polyene to adopt different conformations within the enzyme pocket. This feature enables Lsd18 to epoxidate both of the C═C groups. Additionally, a subpocket located near the Lsd18 active site controls stereoselectivity by dictating which face of the C═C group is placed next to the flavin. Molecular understanding of how Lsd18 transforms a polyene into a bisepoxide during lasalocid A biosynthesis lays the foundation for the production of designer polyethers for drug development.

Phytochemical inhibitors of squalene epoxidase: Integrated In silico and In vitro mechanistic insights for targeting cholesterol biosynthesis

Squalene epoxidase (SQLE) is a critical enzyme in the sterol biosynthesis pathway and a promising therapeutic target for various diseases. This study investigates the inhibitory potential of six phytochemicals, amentoflavone, dihydromyricetin, withaferin A, ursolic acid, paeonol, and maslinic acid, against SQLE through an integrated approach combining in silico predictions and experimental validation. Computational analyses, including molecular docking, molecular dynamics (MD) simulations, Potential energy landscape (PEL), MM/PBSA analysis, and ADMET profiling, identified amentoflavone, dihydromyricetin, and withaferin A as the most promising inhibitors, with high binding affinities and stable interactions within the SQLE binding site. Among these, amentoflavone exhibited the strongest binding affinity (-10.4 kcal/mol), binding free energy (-42.01 ± 2.78 kcal/mol), and stability during a 300 ns MD simulation, supported by favorable MD trajectory and interaction energy profiles. Experimental in vitro assays further validated these findings, showing that all tested compounds exhibited inhibitory activity against SQLE, with amentoflavone demonstrating the lowest IC50 (1.92 ± 0.28 μM), confirming its role as a potent inhibitor. Enzyme kinetics studies revealed that maslinic acid and ursolic acid exhibited noncompetitive inhibition, while withaferin A, paeonol, and amentoflavone acted as competitive inhibitors. Dihydromyricetin demonstrated a mixed inhibition mode due to its dual interaction with the enzyme's active and allosteric sites. The pharmacokinetic analysis indicated that all compounds exhibited drug-like properties, with varying ADMET profiles influencing their potential as therapeutic candidates. This study highlights the therapeutic potential of amentoflavone, withaferin A, and dihydromyricetin as potent SQLE inhibitors, underscoring the value of integrated in silico and in vitro approaches in drug discovery.

Mechanistic Insights into Polyphenols-mediated Squalene Epoxidase Inhibition: Computational Models and Experimental Validation for Targeting Cholesterol Biosynthesis

Squalene epoxidase is a key enzyme in sterol biosynthesis, particularly in cholesterol metabolism. Its inhibition has emerged as a promising therapeutic strategy for metabolic disorders, hypercholesterolemia, and certain infections. Herein, we investigated the SQLE inhibitory potential of six polyphenolic compounds, identified through in silico virtual screening of a large natural phenolic library and selected for high predicted binding affinity and structural diversity. Molecular docking demonstrated strong interactions between these candidates and SQLE, with curcumin exhibiting the highest binding affinity (-10.1 kcal/mol). Molecular dynamics simulations confirmed stable interactions for all compounds, highlighting curcumin, piceatannol, and pterostilbene as particularly favorable. Their strong binding free energies were further supported by MM/PBSA calculations (-36.62 ± 4.17, -31.32 ± 3.77, and -32.01 ± 1.34 kcal/mol, respectively), corroborated by free energy landscape analysis. ADMET profiling revealed diverse pharmacokinetic properties among the six polyphenolics. In vitro testing confirmed curcumin as the most potent inhibitor (IC50 = 1.88 ± 0.21 µM), with piceatannol (2.55 ± 0.30 µM) and pterostilbene (2.69 ± 0.11 µM) following closely. Enzyme kinetics demonstrated that these three compounds act as competitive inhibitors targeting the enzyme's active site. Collectively, these findings highlight the combined power of computational and experimental approaches for identifying novel SQLE inhibitors.

SQLE-catalyzed squalene metabolism promotes mitochondrial biogenesis and tumor development in K-ras-driven cancer

It is well known that activation of oncogenic K-ras alone is insufficient to drive tumor development and that additional factors are needed for full malignant transformation, but the metabolic pathways and regulatory mechanisms that facilitate K-ras-driven cancer development remain to be characterized. Here we show that SQLE, a key enzyme in cholesterol synthesis, is upregulated in K-ras-driven cancer and its high expression is correlated with poor clinical outcome. K-ras regulates SQLE expression in a biphasic manner through reactive oxygen species and MYC signaling. Surprisingly, the pro-oncogenic role of SQLE is not mediated by promoting cholesterol synthesis, but by metabolic removal of squalene and thus mitigating its suppressive effect on the PGC-1α-mediated mitochondrial biogenesis and metabolism. Genetic silencing of SQLE in pancreatic cancer cells causes an accumulation of cellular squalene, which binds to Sp1 protein and causes a formation of a tight Sp1-TFAP2E promoter DNA complex with a highly negative binding score. This aberrant squalene/Sp1/TFAP2E promoter complex hinders the expression of TFAP2E and its downstream molecule PGC-1α, leading to suppression of mitochondrial metabolism and an almost complete inhibition of tumor formation in vivo. Importantly, administration of pharmacological squalene to mice bearing pancreatic cancer xenografts could significantly inhibit tumor growth. Our study has revealed a previously unrecognized role of SQLE in regulating gene expression and mitochondrial metabolism to facilitate K-ras-driven cancer development, and identified SQLE as a novel therapeutic target for potential treatment of pancreatic cancer.

Mechanistic and molecular insights into iterative triepoxidation catalyzed by monooxygenase MonCI using a natural substrate analog

Monensin, a polyether antibiotic produced by Streptomyces cinnamonensis, is synthesized through a series of stereospecific epoxidations orchestrated by the FAD-dependent monooxygenase MonCI. This study presents the crystal structure of MonCI in complex with a substrate analog, farnesyl acetate, which undergoes in vitro epoxidation at all three olefinic sites by MonCI. Additionally, we have solved the crystal structures of MonCI in complex with mono- and bis-epoxide intermediates. Structural analysis revealed that the interactions between MonCI and its substrate are predominantly hydrophobic, with residue Y208 playing a crucial role in substrate translocation. Computational modeling emphasizes the importance of FAD proximity to each olefinic group for efficient catalysis, providing insight into the mechanistic pathways for the first, second, and third epoxidations. Notably, when combined with electrochemical techniques, the yield of tri-epoxide farnesyl acetate reached 94 %, surpassing traditional enzymatic catalysis. This work not only elucidates the catalytic mechanism of MonCI but also underscores its potential as an effective biocatalyst for processive epoxidation in organic synthesis.

The Role of Cholesterol Metabolism and Its Regulation in Tumor Development

BACKGROUND

Within the tumor microenvironment, tumor cells undergo metabolic reprogramming of cholesterol due to intrinsic cellular alterations and changes in the extracellular milieu. Furthermore, cholesterol reprogramming within this microenvironment influences the immune landscape of tumors, facilitating immune evasion and consequently promoting tumorigenesis. These biological changes involve modifications in numerous enzymes associated with cholesterol uptake and synthesis, including NPC1L1, SREBP, HMGCR, SQLE, and PCSK9.

REVIEW

This review systematically summarizes the role of cholesterol metabolism and its associated enzymes in cancer progression, examines the mechanisms through which dysregulation of cholesterol metabolism affects immune cells within the tumor microenvironment, and discusses recent advancements in cancer therapies that target cholesterol metabolism.

CONCLUSION

Targeting cholesterol metabolism-related enzymes can inhibit tumor growth, reshape immune landscapes, and rejuvenate antitumor immunity, offering potential therapeutic avenues in cancer treatment.

Disturbing Cholesterol/Sphingolipid Metabolism by Squalene Epoxidase Arises Crizotinib Hepatotoxicity

Metabolic disorders have been identified as one of the causes of drug-induced liver injury; however, the direct regulatory mechanism regarding this disorder has not yet been clarified. In this study, a single regulatory mechanism of small molecule kinase inhibitors, with crizotinib as the representative drug is elucidated. First, it is discovered that crizotinib induced aberrant lipid metabolism and apoptosis in the liver. A mechanistic study revealed that crizotinib treatment promoted the accumulation of squalene epoxidase (SQLE) by inhibiting autophagosome-lysosome fusion which blocked the autophagic degradation of SQLE. A maladaptive increase in SQLE led to disturbances in cholesterol and sphingolipid metabolism via an enzymatic activity-dependent manner. Abnormal cholesterol results in both steatosis and inflammatory infiltration, and disturbances in sphingolipid metabolism promote cell apoptosis by inducing lysosomal membrane permeabilization. The restoration of the level or activity of SQLE ameliorated steatosis and hepatocyte injury. The autophagy activator known as metformin or the SQLE enzymatic inhibitor known as terbinafine has potential clinical use for alleviating crizotinib hepatotoxicity.

Coenzyme Q10 deficiency disrupts lipid metabolism by altering cholesterol homeostasis in neurons

Coenzyme Q10 (CoQ10) is a critical component of the mitochondrial respiratory chain. CoQ10 deficiencies cause a variety of clinical syndromes, often involving encephalopathies. The heterogeneity of clinical manifestations implies different pathomechanisms, reflecting CoQ10 involvement in several biological processes. One such process is cholesterol homeostasis, since CoQ10 is synthesized through the mevalonate pathway, which also produces cholesterol. To elucidate the role of lipid dysfunction in the pathogenesis of CoQ10 deficiency, we investigated lipid metabolism in human CoQ10 deficient iPSCs-derived neurons, and in SH-SY5Y neurons after pharmacological manipulation of the mevalonate pathway. We show that CoQ10 deficiency causes alterations in cholesterol homeostasis, fatty acids oxidation, phospholipids and sphingolipids synthesis in neurons. These alterations depend on the molecular defect, and on the residual CoQ10 levels. Our results imply that CoQ10 deficiencies can induce pathology by altering lipid homeostasis and the composition of cellular membranes. These findings provide further understanding of the mechanisms underlying CoQ10 deficiency and point to potential novel therapeutic targets.

Exploring quinoline-type inhibitors of ergosterol biosynthesis: Binding mechanism investigation via molecular docking, pharmacophore mapping, and dynamics simulation approaches

Drug-resistant fungal infections pose a formidable challenge in healthcare, attributed to ergosterol production as a key mechanism of resistance. It is therefore imperative to target this pathway for effective therapeutic interventions. In this study, we have analyzed the binding mode of twelve quinoline derivatives known to be effective against various Candida species, Microsporum gypseum, and Cryptococcus neoformans. Employing molecular docking techniques, pharmacological modeling, and molecular dynamics, we have delved into interactions with Erg1, Erg11, and Erg24 proteins, crucial in ergosterol biosynthesis. Our analysis unveiled critical interactions that facilitate the docking and stabilization of C-2-substituted quinoline derivatives on these proteins, highlighting their potential as regulators of ergosterol synthesis. Furthermore, complexes formed with Erg1 … 8 (MIC = 125 μg/mL) and Erg24 … 4 (MIC = 62 μg/mL) showed higher affinity and stability during the docking process, pointing to their promising role as regulatory agents of these proteins. This in silico approach provides insights into potential pathways to combat drug-resistant fungal infections.

Multi-pronged molecular insights into flavonoid-mediated inhibition of squalene epoxidase: a pathway to novel therapeutics

Squalene epoxidase (SQLE) is a crucial enzyme in the sterol biosynthesis pathway and a promising target for therapeutic intervention in hypercholesterolemia and fungal infections. This study evaluates the inhibitory potential of six flavonoids namely silibinin, baicalin, naringenin, chrysin, apigenin-7-O-glucoside, and isorhamnetin against SQLE using an integrative approach combining in silico and experimental methods. Molecular docking revealed that apigenin-7-O-glucoside, silibinin, and baicalin displayed the highest binding affinities (-10.7, -10.2, and -10.0 kcal mol-1, respectively) and robust interactions with the SQLE binding site. These findings were corroborated by 200 ns molecular dynamics (MD) simulations, which demonstrated stable binding trajectories, minimal structural fluctuations, a thermodynamically favored potential energy landscape (PEL) and favorable MM/PBSA binding free energies for three flavonoids. Experimental validation via in vitro inhibition assays confirmed the computational predictions, with apigenin-7-O-glucoside emerging as the most potent inhibitor (IC50 = 1.74 ± 0.05 μM), followed by silibinin (IC50 = 1.88 ± 0.28 μM) and baicalin (IC50 = 2.50 ± 0.46 μM). Enzyme kinetics studies revealed distinct mechanisms of action: apigenin-7-O-glucoside exhibited competitive inhibition, while silibinin and baicalin showed mixed inhibition. Furthermore, in silico ADMET analysis indicated favorable pharmacokinetic and pharmacodynamic profiles for these flavonoids, with silibinin demonstrating particularly high bioavailability and lipophilicity. This study highlights apigenin-7-O-glucoside, silibinin, and baicalin as potent SQLE inhibitors with promising therapeutic potential. The congruence between in silico predictions and experimental results underscores the reliability of computational approaches in drug discovery, paving the way for future preclinical development of these compounds as novel SQLE-targeted therapeutics.

SQLE-mediated squalene metabolism promotes tumor immune evasion in pancreatic cancer

Background

Squalene epoxidase (SQLE) is a key enzyme in cholesterol biosynthesis and has been shown to negatively affect tumor immunity and is associated with poor outcomes of immunotherapy in various cancers. While most research in this area has focused on the impact of cholesterol on immune functions, the influence of SQLE-mediated squalene metabolism within the tumor immune microenvironment (TIME) remains unexplored.

Methods

We established an immune-competent mouse model (C57BL/6) bearing mouse pancreatic cancer xenografts (KPC cells) with or without stable SQLE-knockdown (SQLE-KD) to evaluate the impact of SQLE-mediated metabolism on pancreatic cancer growth and immune functions. The effect of squalene on tumor growth and immune cells was tested by direct administration of squalene to C57BL/6 mice bearing KPC tumors. Flow cytometry analysis and immunohistochemical (IHC) staining of immune cells from the tumor tissues were performed to evaluate changes in immune function. We also employed RNA-sequencing to analyze the gene expression profiles in pancreatic cancer cells (PANC-1) treated with or without squalene. RT-PCR and Western blot analyses were used to investigate the relevant molecular mechanisms.

Results

We show that SQLE is significantly overexpressed in pancreatic cancer, and abrogation of SQLE results in a significant increase in squalene accumulation within tumor cells. The elevated squalene inhibits CXCL1 transcription through its impact on the NF-κB pathway via p65, and thus reduces the recruitment of myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs) into the tumor microenvironment. Silencing of SQLE also leads to an increased proportion of CD8+ T cells in the tumor tissues and suppresses tumor growth in vivo. Importantly, direct administration of squalene, the metabolic substrate of SQLE, to immune-competent mice bearing KPC pancreatic cancer tumors causes a substantial decrease in CD206+ TAMs and MDSCs, thus releasing immune suppression and inhibiting tumor growth.

Conclusion

Our study shows that squalene is an important immune-modulating metabolite that inhibits the infiltration of immune-suppressive cells in TIME, and that SQLE exerts its tumor immune evasion effect by metabolic removal of squalene. Thus, SQLE-mediated squalene metabolic pathway could be a potential target to enhance antitumor immunity in pancreatic cancer.

Screening, optimization, and ADMET evaluation of HCJ007 for pancreatic cancer treatment through active learning and dynamics simulation

In this study, we leveraged a sophisticated active learning model to enhance virtual screening for SQLE inhibitors. The model's improved predictive accuracy identified compounds with significant advantages in binding affinity and thermodynamic stability. Detailed analyses, including molecular dynamics simulations and ADMET profiling, were conducted, particularly focusing on compounds CMNPD11566 and its derivative HCJ007. CMNPD11566 showed stable interactions with SQLE, while HCJ007 exhibited improved binding stability and more frequent interactions with key residues, indicating enhanced dynamic adaptability and overall binding effectiveness. ADMET data comparison highlighted HCJ007s superior profile in terms of lower toxicity and better drug-likeness. Our findings suggest HCJ007 as a promising candidate for SQLE inhibition, with significant improvements over CMNPD11566 in various pharmacokinetic and safety parameters. The study underscores the efficacy of computational models in drug discovery and the importance of comprehensive preclinical evaluations.

Targeting squalene epoxidase in the treatment of metabolic-related diseases: current research and future directions

Metabolic-related diseases are chronic diseases caused by multiple factors, such as genetics and the environment. These diseases are difficult to cure and seriously affect human health. Squalene epoxidase (SQLE), the second rate-limiting enzyme in cholesterol synthesis, plays an important role in cholesterol synthesis and alters the gut microbiota and tumor immunity. Research has shown that SQLE is expressed in many tissues and organs and is involved in the occurrence and development of various metabolic-related diseases, such as cancer, nonalcoholic fatty liver disease, diabetes mellitus, and obesity. SQLE inhibitors, such as terbinafine, NB598, natural compounds, and their derivatives, can effectively ameliorate fungal infections, nonalcoholic fatty liver disease, and cancer. In this review, we provide an overview of recent research progress on the role of SQLE in metabolic-related diseases. Further research on the regulation of SQLE expression is highly important for developing drugs for the treatment of metabolic-related diseases with good pharmacological activity.

Functional Redundancy and Dual Function of a Hypothetical Protein in the Biosynthesis of Eunicellane-Type Diterpenoids

Many complex terpenoids, predominantly isolated from plants and fungi, show drug-like physicochemical properties. Recent advances in genome mining revealed actinobacteria as an almost untouched treasure trove of terpene biosynthetic gene clusters (BGCs). In this study, we characterized a terpene BGC with an unusual architecture. The selected BGC includes, among others, genes encoding a terpene cyclase fused to a truncated reductase domain and a cytochrome P450 monooxygenase (P450) that is split over three gene fragments. Functional characterization of the BGC in a heterologous host led to the identification of several new members of the trans-eunicellane family of diterpenoids, the euthailols, that feature unique oxidation patterns. A combination of bioinformatic analyses, structural modeling studies, and heterologous expression revealed a dual function of the pathway-encoded hypothetical protein that acts as an isomerase and an oxygenase. Moreover, in the absence of other tailoring enzymes, a P450 hydroxylates the eunicellane scaffold at a position that is not modified in other eunicellanes. Surprisingly, both the modifications installed by the hypothetical protein and one of the P450s exhibit partial redundancy. Bioactivity assays revealed that some of the euthailols show growth inhibitory properties against Gram-negative ESKAPE pathogens. The characterization of the euthailol BGC in this study provides unprecedented insights into the partial functional redundancy of tailoring enzymes in complex diterpenoid biosynthesis and highlights hypothetical proteins as an important and largely overlooked family of tailoring enzymes involved in the maturation of complex terpenoids.

Targeting squalene epoxidase restores anti-PD-1 efficacy in metabolic dysfunction-associated steatohepatitis-induced hepatocellular carcinoma

OBJECTIVE

Squalene epoxidase (SQLE) promotes metabolic dysfunction-associated steatohepatitis-associated hepatocellular carcinoma (MASH-HCC), but its role in modulating the tumour immune microenvironment in MASH-HCC remains unclear.

DESIGN

We established hepatocyte-specific Sqle transgenic (tg) and knockout mice, which were subjected to a choline-deficient high-fat diet plus diethylnitrosamine to induce MASH-HCC. SQLE function was also determined in orthotopic and humanised mice. Immune landscape alterations of MASH-HCC mediated by SQLE were profiled by single-cell RNA sequencing and flow cytometry.

RESULTS

Hepatocyte-specific Sqle tg mice exhibited a marked increase in MASH-HCC burden compared with wild-type littermates, together with decreased tumour-infiltrating functional IFN-γ+ and Granzyme B+ CD8+ T cells while enriching Arg-1+ myeloid-derived suppressor cells (MDSCs). Conversely, hepatocyte-specific Sqle knockout suppressed tumour growth with increased cytotoxic CD8+ T cells and reduced Arg-1+ MDSCs, inferring that SQLE promotes immunosuppression in MASH-HCC. Mechanistically, SQLE-driven cholesterol accumulation in tumour microenvironment underlies its effect on CD8+ T cells and MDSCs. SQLE and its metabolite, cholesterol, impaired CD8+ T cell activity by inducing mitochondrial dysfunction. Cholesterol depletion in vitro abolished the effect of SQLE-overexpressing MASH-HCC cell supernatant on CD8+ T cell suppression and MDSC activation, whereas cholesterol supplementation had contrasting functions on CD8+ T cells and MDSCs treated with SQLE-knockout supernatant. Targeting SQLE with genetic ablation or pharmacological inhibitor, terbinafine, rescued the efficacy of anti-PD-1 treatment in MASH-HCC models.

CONCLUSION

SQLE induces an impaired antitumour response in MASH-HCC via attenuating CD8+ T cell function and augmenting immunosuppressive MDSCs. SQLE is a promising target in boosting anti-PD-1 immunotherapy for MASH-HCC.

Diverse antifungal potency of terbinafine as a therapeutic agent against Exophiala dermatitidis in vitro

Exophiala dermatitidis (E. dermatitidis), which causes skin or respiratory disease, is occasionally fatal in immunocompromised patients. Here, we report the unique antifungal potency of terbinafine (TRB), which targets squalene epoxidase, against E. dermatitidis (SQLEED) using various in vitro approaches. The versatile antifungal activities, including fungicidal activity, biofilm formation inhibition, biofilm eradication activity, and the combination effect of TRB, posaconazole (PSC), and amphotericin B (AmB) with great antifungal potency against E. dermatitidis were evaluated using crystal violet and cell viability assay. TRB formed an H-bond through Y102 in SQLEED in the binding model. E. dermatitidis hyphae elongated and attached to a cell scaffold, forming a membrane-like biofilm. TRB and PSC showed more potent antibiofilm activities than AmB, and exhibited post-antifungal effects without incubation against E. dermatitidis conidia, reducing growth at lower concentrations. In contrast, AmB exhibited strong dose- and time-dependent killing and biofilm-eradication activities. The combination of TRB and PSC was more effective than that of TRB and AmB or PSC and AmB. Although the tissue migration of TRB must be considered, these data suggest that TRB and PSC may be useful agents and a potent combination in severely immunocompromised patients with refractory and systemic E. dermatitidis infection.

Reengineering the Substrate Tunnel to Enhance the Catalytic Efficiency of Squalene Epoxidase

Squalene epoxidase plays a pivotal role in the biosynthesis of ergosterol, its derivatives, and other triterpenoid compounds by catalyzing the transformation of squalene into 2,3-oxidosqualene. However, its low catalytic efficiency remains a primary bottleneck for the microbial synthesis of triterpenoids. In this study, the catalytic activity of the squalene epoxidase from Saccharomyces cerevisiae was significantly improved by reshaping its substrate tunnel, resulting in a marked increase in the yield of the final product, ergosterol. First, the amino acid in the catalytic pocket of squalene epoxidase was replaced with alanine (Ala), effectively reducing the steric hindrance, and thus, enhancing the affinity of the enzyme with its substrate. Then, the V249H/L343A mutant was obtained by redesigning the substrate tunnel of dominant mutant L343A, thus, increasing the titer of ergosterol. The study also elucidated the mechanism behind the increased catalytic activity of the V249H/L343A mutant through substrate tunnel parameter analysis and molecular dynamics simulations. Finally, a titer of 3345 mg/L of ergosterol was achieved by strains containing V249H/L343A in a 5 L bioreactor, with a specific yield of 84 mg/g dry cell weight (DCW), marking a 64% increase compared with the titer achieved by wild type strains. This study established a strong foundation for improving the synthetic efficiency of ergosterol and other triterpenoid compounds.

Structural and Functional Characterization of a Novel Class A Flavin Monooxygenase from Bacillus niacini

A gene cluster responsible for the degradation of nicotinic acid (NA) in Bacillus niacini has recently been identified, and the structures and functions of the resulting enzymes are currently being evaluated to establish pathway intermediates. One of the genes within this cluster encodes a flavin monooxygenase (BnFMO) that is hypothesized to catalyze a hydroxylation reaction. Kinetic analyses of the recombinantly purified BnFMO suggest that this enzyme catalyzes the hydroxylation of 2,6-dihydroxynicotinic acid (2,6-DHNA) or 2,6-dihydroxypyridine (2,6-DHP), which is formed spontaneously by the decarboxylation of 2,6-DHNA. To understand the details of this hydroxylation reaction, we determined the structure of BnFMO using a multimodel approach combining protein X-ray crystallography and cryo-electron microscopy (cryo-EM). A liganded BnFMO cryo-EM structure was obtained in the presence of 2,6-DHP, allowing us to make predictions about potential catalytic residues. The structural data demonstrate that BnFMO is trimeric, which is unusual for Class A flavin monooxygenases. In both the electron density and coulomb potential maps, a region at the trimeric interface was observed that was consistent with and modeled as lipid molecules. High-resolution mass spectral analysis suggests that there is a mixture of phosphatidylethanolamine and phosphatidylglycerol lipids present. Together, these data provide insights into the molecular details of the central hydroxylation reaction unique to the aerobic degradation of NA in Bacillus niacini.

Cholesterol inhibition enhances antitumor response of gilteritinib in lung cancer cells

Repositioning approved antitumor drugs for different cancers is a cost-effective approach. Gilteritinib was FDA-approved for the treatment of FLT3-mutated acute myeloid leukemia in 2018. However, the therapeutic effects and mechanism of Gilteritinib on other malignancies remain to be defined. In this study, we identified that gilteritinib has an inhibitory effect on lung cancer cells (LCCs) without FLT3 mutation in vitro and in vivo. Unexpectedly, we found that gilteritinib induces cholesterol accumulation in LCCs via upregulating cholesterol biosynthetic genes and inhibiting cholesterol efflux. This gilteritinib-induced cholesterol accumulation not only attenuates the antitumor effect of gilteritinib but also induces gilteritinib-resistance in LCCs. However, when cholesterol synthesis was prevented by squalene epoxidase (SQLE) inhibitor NB-598, both LCCs and gilteritinib-resistant LCCs became sensitive to gilteritinib. More importantly, the natural cholesterol inhibitor 25-hydroxycholesterol (25HC) can suppress cholesterol biosynthesis and increase cholesterol efflux in LCCs. Consequently, 25HC treatment significantly increases the cytotoxicity of gilteritinib on LCCs, which can be rescued by the addition of exogenous cholesterol. In a xenograft model, the combination of gilteritinib and 25HC showed significantly better efficacy than either monotherapy in suppressing lung cancer growth, without obvious general toxicity. Thus, our findings identify an increase in cholesterol induced by gilteritinib as a mechanism for LCC survival, and highlight the potential of combining gilteritinib with cholesterol-lowering drugs to treat lung cancer.

Single-nucleus transcriptomics and chromatin accessibility analysis of musk gland development in Chinese forest musk deer (Moschus berezovskii)

Musk secreted by male forest musk deer (Moschus berezovskii) musk glands is an invaluable component of medicine and perfume. Musk secretion depends on musk gland maturation; however, the mechanism of its development remains elusive. Herein, using single cell multiome ATAC + gene expression coupled with several bioinformatic analyses, a dynamic transcriptional cell atlas of musk gland development was revealed, and key genes and transcription factors affecting its development were determined. Twelve cell types, including two different types of acinar cells (Clusters 0 and 10) were identified. Single-nucleus RNA and single-nucleus ATAC sequencing analyses revealed that seven core target genes associated with musk secretion (Hsd17b2, Acacb, Lss, Vapa, Aldh16a1, Aldh7a1, and Sqle) were regulated by 12 core transcription factors (FOXO1, CUX2, RORA, RUNX1, KLF6, MGA, NFIC, FOXO3, ETV5, NR3C1, HSF4, and MITF) during the development of Cluster 0 acinar cells. Kyoto Encyclopedia of Genes and Genomes enrichment showed significant changes in the pathways associated with musk secretion during acinar cell development. Gene set variation analysis also revealed that certain pathways associated with musk secretion were enriched in 6-year-old acinar cells. A gene co-expression network was constructed during acinar cell development to provide a precise understanding of the connections between transcription factors, genes, and pathways. Finally, intercellular communication analysis showed that intercellular communication is involved in musk gland development. This study provides crucial insights into the changes and key factors underlying musk gland development, which serve as valuable resources for studying musk secretion mechanisms and promoting the protection of this endangered species.

Clinical Course, Antifungal Susceptibility, and Genomic Sequencing of Trichophyton indotineae

Importance

Trichophyton indotineae is an emerging dermatophyte causing outbreaks of extensive tinea infections often unresponsive to terbinafine. This species has been detected worldwide and in multiple US states, yet detailed US data on infections with T indotineae are sparse and could improve treatment practices and medical understanding of transmission.

Objective

To correlate clinical features of T indotineae infections with in vitro antifungal susceptibility testing results, squalene epoxidase gene sequence variations, and isolate relatedness using whole-genome sequencing.

Design, Setting, and Participants

This retrospective cohort study of patients with T indotineae infections in New York City spanned May 2022 to May 2023. Patients with confirmed T indotineae infections were recruited from 6 New York City medical centers.

Main Outcome and Measure

Improvement or resolution at the last follow-up assessment.

Results

Among 11 patients with T indotineae (6 male and 5 female patients; median [range] age, 39 [10-65] years), 2 were pregnant; 1 had lymphoma; and the remainder were immunocompetent. Nine patients reported previous travel to Bangladesh. All had widespread lesions with variable scale and inflammation, topical antifungal monotherapy failure, and diagnostic delays (range, 3-42 months). Terbinafine treatment failed in 7 patients at standard doses (250 mg daily) for prolonged duration; these patients also had isolates with amino acid substitutions at positions 393 (L393S) or 397 (F397L) in squalene epoxidase that correlated with elevated terbinafine minimum inhibitory concentrations of 0.5 μg/mL or higher. Patients who were treated with fluconazole and griseofulvin improved in 2 of 4 and 2 of 5 instances, respectively, without correlation between outcomes and antifungal minimum inhibitory concentrations. Furthermore, 5 of 7 patients treated with itraconazole cleared or had improvement at the last follow-up, and 2 of 7 were lost to follow-up or stopped treatment. Based on whole-genome sequencing analysis, US isolates formed a cluster distinct from Indian isolates.

Conclusion and Relevance

The results of this case series suggest that disease severity, diagnostic delays, and lack of response to typically used doses and durations of antifungals for tinea were common in this primarily immunocompetent patient cohort with T indotineae, consistent with published data. Itraconazole was generally effective, and the acquisition of infection was likely in Bangladesh.

Depletion of squalene epoxidase in synergy with glutathione peroxidase 4 inhibitor RSL3 overcomes oxidative stress resistance in lung squamous cell carcinoma

Background

Lung squamous cell carcinoma (LUSC) lacks effective targeted therapies and has a poor prognosis. Disruption of squalene epoxidase (SQLE) has been implicated in metabolic disorders and cancer. However, the role of SQLE as a monooxygenase involved in oxidative stress remains unclear.

Methods

We analyzed the expression and prognosis of lung adenocarcinoma (LUAD) and LUSC samples from GEO and TCGA databases. The proliferative activity of the tumors after intervention of SQLE was verified by cell and animal experiments. JC-1 assay, flow cytometry, and Western blot were used to show changes in apoptosis after intervention of SQLE. Flow cytometry and fluorescence assay of ROS levels were used to indicate oxidative stress status.

Results

We investigated the unique role of SQLE expression in the diagnosis and prognosis prediction of LUSC. Knockdown of SQLE or treatment with the SQLE inhibitor terbinafine can suppress the proliferation of LUSC cells by inducing apoptosis and reactive oxygen species accumulation. However, depletion of SQLE also results in the impairment of lipid peroxidation and ferroptosis resistance such as upregulation of glutathione peroxidase 4. Therefore, prevention of SQLE in synergy with glutathione peroxidase 4 inhibitor RSL3 effectively mitigates the proliferation and growth of LUSC.

Conclusion

Our study indicates that the low expression of SQLE employs adaptive survival through regulating the balance of apoptosis and ferroptosis resistance. In future, the combinational therapy of targeting SQLE and ferroptosis could be a promising approach in treating LUSC.

A review on potential therapeutic targets for the treatment of leishmaniasis

Leishmania, a protozoan parasite, is responsible for the occurrence of leishmaniasis, a disease that is prevalent in tropical regions. Visceral Leishmaniasis (VL), also known as kala-azar in Asian countries, is one of the most significant forms of VL, along with Cutaneous Leishmaniasis (CL) and Mucocutaneous Leishmaniasis (ML). Management of this condition typically entails the use of chemotherapy as the sole therapeutic option. The current treatments for leishmaniasis present several drawbacks, including a multitude of side effects, prolonged treatment duration, disparate efficacy across different regions, and the emergence of resistance. To address this urgent need, it is imperative to identify alternative treatments that are both safer and more effective. The identification of appropriate pharmacological targets in conjunction with biological pathways constitutes the initial stage of drug discovery. In this review, we have addressed the key metabolic pathways that represent potential pharmacological targets as well as prominent treatment options for leishmaniasis.

The constitutively active form of a key cholesterol synthesis enzyme is lipid droplet-localized and upregulated in endometrial cancer tissues

Cholesterol is essential for both normal cell viability and cancer cell proliferation. Aberrant activity of squalene monooxygenase (SM, also known as squalene epoxidase), the rate-limiting enzyme of the committed cholesterol synthesis pathway, is accordingly implicated in a growing list of cancers. We previously reported that hypoxia triggers the truncation of SM to a constitutively active form, thus preserving sterol synthesis during oxygen shortfalls. Here, we show SM truncation is upregulated and correlates with the magnitude of hypoxia in endometrial cancer tissues, supporting the in vivo relevance of our earlier work. To further investigate the pathophysiological consequences of SM truncation, we examined its lipid droplet-localized pool using complementary immunofluorescence and cell fractionation approaches and found that it exclusively comprises the truncated enzyme. This partitioning is facilitated by the loss of an endoplasmic reticulum-embedded region at the SM N terminus, whereas the catalytic domain containing membrane-associated C-terminal helices is spared. Moreover, we determined multiple amphipathic helices contribute to the lipid droplet localization of truncated SM. Taken together, our results expand on the striking differences between the two forms of SM and suggest upregulated truncation may contribute to SM-related oncogenesis.

Squalene Epoxidase: Its Regulations and Links with Cancers

Squalene epoxidase (SQLE) is a key enzyme in the mevalonate-cholesterol pathway that plays a critical role in cellular physiological processes. It converts squalene to 2,3-epoxysqualene and catalyzes the first oxygenation step in the pathway. Recently, intensive efforts have been made to extend the current knowledge of SQLE in cancers through functional and mechanistic studies. However, the underlying mechanisms and the role of SQLE in cancers have not been fully elucidated yet. In this review, we retrospected current knowledge of SQLE as a rate-limiting enzyme in the mevalonate-cholesterol pathway, while shedding light on its potential as a diagnostic and prognostic marker, and revealed its therapeutic values in cancers. We showed that SQLE is regulated at different levels and is involved in the crosstalk with iron-dependent cell death. Particularly, we systemically reviewed the research findings on the role of SQLE in different cancers. Finally, we discussed the therapeutic implications of SQLE inhibitors and summarized their potential clinical values. Overall, this review discussed the multifaceted mechanisms that involve SQLE to present a vivid panorama of SQLE in cancers.

Innovations in Antifungal Drug Discovery among Cell Envelope Synthesis Enzymes through Structural Insights

Life-threatening systemic fungal infections occur in immunocompromised patients at an alarming rate. Current antifungal therapies face challenges like drug resistance and patient toxicity, emphasizing the need for new treatments. Membrane-bound enzymes account for a large proportion of current and potential antifungal targets, especially ones that contribute to cell wall and cell membrane biosynthesis. Moreover, structural biology has led to a better understanding of the mechanisms by which these enzymes synthesize their products, as well as the mechanism of action for some antifungals. This review summarizes the structures of several current and potential membrane-bound antifungal targets involved in cell wall and cell membrane biosynthesis and their interactions with known inhibitors or drugs. The proposed mechanisms of action for some molecules, gleaned from detailed inhibitor-protein studeis, are also described, which aids in further rational drug design. Furthermore, some potential membrane-bound antifungal targets with known inhibitors that lack solved structures are discussed, as these might be good enzymes for future structure interrogation.

RNA sequencing unravels novel L cell constituents and mechanisms of GLP-1 secretion in human gastric bypass-operated intestine

AIMS/HYPOTHESIS

Roux-en-Y gastric bypass surgery (RYGB) frequently results in remission of type 2 diabetes as well as exaggerated secretion of glucagon-like peptide-1 (GLP-1). Here, we assessed RYGB-induced transcriptomic alterations in the small intestine and investigated how they were related to the regulation of GLP-1 production and secretion in vitro and in vivo.

METHODS

Human jejunal samples taken perisurgically and 1 year post RYGB (n=13) were analysed by RNA-seq. Guided by bioinformatics analysis we targeted four genes involved in cholesterol biosynthesis, which we confirmed to be expressed in human L cells, for potential involvement in GLP-1 regulation using siRNAs in GLUTag and STC-1 cells. Gene expression analyses, GLP-1 secretion measurements, intracellular calcium imaging and RNA-seq were performed in vitro. OGTTs were performed in C57BL/6j and iScd1-/- mice and immunohistochemistry and gene expression analyses were performed ex vivo.

RESULTS

Gene Ontology (GO) analysis identified cholesterol biosynthesis as being most affected by RYGB. Silencing or chemical inhibition of stearoyl-CoA desaturase 1 (SCD1), a key enzyme in the synthesis of monounsaturated fatty acids, was found to reduce Gcg expression and secretion of GLP-1 by GLUTag and STC-1 cells. Scd1 knockdown also reduced intracellular Ca2+ signalling and membrane depolarisation. Furthermore, Scd1 mRNA expression was found to be regulated by NEFAs but not glucose. RNA-seq of SCD1 inhibitor-treated GLUTag cells identified altered expression of genes implicated in ATP generation and glycolysis. Finally, gene expression and immunohistochemical analysis of the jejunum of the intestine-specific Scd1 knockout mouse model, iScd1-/-, revealed a twofold higher L cell density and a twofold increase in Gcg mRNA expression.

CONCLUSIONS/INTERPRETATION

RYGB caused robust alterations in the jejunal transcriptome, with genes involved in cholesterol biosynthesis being most affected. Our data highlight SCD as an RYGB-regulated L cell constituent that regulates the production and secretion of GLP-1.

Knockdown of SQLE promotes CD8+ T cell infiltration in the tumor microenvironment

Cholesterol biosynthesis and metabolism are critical aspects that shape the process of tumor development and associated microenvironmental conditions owing to the ability of cholesterol to drive tumor growth and invasion. Squalene Epoxidase (SQLE) is the second rate-limiting enzyme involved in the synthesis of cholesterol. The functional role of SQLE within the tumor microenvironment, however, has yet to be established. Here we show that SQLE is distinctively expressed across most types of cancer, and the expression level is highly correlated with tumor mutation burden and microsatellite instability. Accordingly, SQLE was identified as a prognostic risk factor in cancer patients. In addition, we observed a negative correlation between SQLE expression and immune cell infiltration across multiple cancers, and murine xenograft model further confirmed that SQLE knockdown was associated with enhanced intratumoral CD8+ T cell infiltration. Using next-generation sequencing, we identified 410 genes distinctively expressed in tumors exhibiting SQLE inhibition. KEGG and GO analysis further verified that SQLE altered the immune response in the tumor microenvironment. Furthermore, we found that the metabolism and translation of proteins is the main binding factor with SQLE. Our findings ascertain that SQLE is a potential target in multiple cancers and suppressing SQLE establishes an essential mechanism for shaping tumor microenvironment.

Squalene epoxidase promotes breast cancer progression by regulating CCNB1 protein stability

BACKGROUND

Breast cancer (BC) is a prevalent malignancy affecting women, characterized by a substantial occurrence rate. Squalene epoxidase (SQLE) is a crucial regulator of ferroptosis and has been associated with promoting cell growth and invasion in different types of human cancers. This study aimed to investigate the functional significance of SQLE in BC and elucidate the underlying molecular mechanisms involved.

METHODS

SQLE expression levels in BC tissues were evaluated using quantitative real-time polymerase chain reaction, western blotting, and immunohistochemistry. Cell viability, invasion, migration, and cell cycle distribution were assessed using a combination of assays, including the Cell Counting Kit-8, EdU, colony formation, Transwell, and wound healing assays and flow cytometry analysis. Measurement of intracellular reactive oxygen species (ROS), malondialdehyde assay, and glutathione assay were utilized to investigate ferroptosis. Furthermore, co-immunoprecipitation and immunofluorescence assays were conducted to explore the correlation between SQLE and CCNB1. The in vivo tumor growth was evaluated by conducting a xenograft tumorigenicity assay to investigate the impact of SQLE.

RESULTS

SQLE expression was significantly increased in BC, and higher SQLE expression levels were significantly associated with an unfavorable prognosis. In vitro functional assays revealed that the overexpression of SQLE markedly enhanced the proliferation, migration, and invasion capacities of BC cells. Furthermore, SQLE overexpression facilitated tumor growth in nude mice. Mechanistically, SQLE alleviated the ubiquitination modification of CCNB1, leading to enhanced stability of the CCNB1 protein and decreased intracellular ROS levels. Ultimately, this inhibited ferroptosis and facilitated the progression of BC. Our findings have provided insights into a crucial pathway by which elevated SQLE expression confers protection to BC cells against ferroptosis, thus promoting cancer progression. SQLE may serve as a novel oncological marker and a potential therapeutic target for BC progression.

CONCLUSIONS

In conclusion, this study provides evidence that SQLE plays a regulatory role in BC progression by modulating CCNB1 and ferroptosis. These findings offer valuable insights into the role of SQLE in the pathogenesis of BC and demonstrate its potential as a therapeutic target for treating BC.

Investigation of the response of Platycodongrandiflorus (Jacq.) A. DC to salt stress using combined transcriptomics and metabolomics

BACKGROUND

Platycodon grandiflorus (Jacq.) A. DC is a famous traditional Chinese medicine in China and an authentic medicine in Inner Mongolia. It has been traditionally used as an expectorant in cough and also has anti-inflammatory and other pharmacological effects. As a homologous plant of medicine and food, P. grandiflorus is widely planted in Northeast China. Soil salinity isa limiting factor for its cultivation. In this study, we comprehensively described the physiological characteristics of P. grandiflorus and combined transcriptomics and metabolomics to study the response of roots of P. grandiflorus to salt stress.

RESULTS

Overall, 8,988 differentially expressed genes were activated and significantly altered the metabolic processes. In total, 428 differentially abundant metabolites were affected by salt stress. After moderate and severe salt stress, most of the differentially abundant metabolites were enriched in the L-phenylalanine metabolic pathway. Through the comprehensive analysis of the interaction between key genes and metabolites, the main pathways such as lignin compound biosynthesis and triterpene saponin biosynthesis were completed. The relative content of compounds related to lignin biosynthesis, such as caffeic acid, coniferin, and syringing, increased under salt stress, and the related genes such as PAL, C4H, and the key enzyme gene UGT72E2 were activated to adapt to the salt stress. Platycodon saponin is one of the major triterpene saponins in P. grandiflorus, and Platycodin D is its most abundant major bioactive component. Under severe salt stress, Platycodin D level increased by nearly 1.77-fold compared with the control group. Most of the genes involved insynthetic pathway of Platycodin D, such as HMGCR, GGPS, SE, and LUP, were upregulated under salt stress.

CONCLUSION

Salt stress led to a decrease in the biomass and affected the activities of antioxidant enzymes and contents of osmotic regulators in the plant. These results provided not only novel insights into the underlying mechanisms of response of P. grandiflorus to salt stress but also a foundation for future studies on the function of genes related to salt tolerance in the triterpenoid saponin biosynthesis pathway.

Triepoxide formation by a flavin-dependent monooxygenase in monensin biosynthesis

Monensin A is a prototypical natural polyether polyketide antibiotic. It acts by binding a metal cation and facilitating its transport across the cell membrane. Biosynthesis of monensin A involves construction of a polyene polyketide backbone, subsequent epoxidation of the alkenes, and, lastly, formation of cyclic ethers via epoxide-opening cyclization. MonCI, a flavin-dependent monooxygenase, is thought to transform all three alkenes in the intermediate polyketide premonensin A into epoxides. Our crystallographic study has revealed that MonCI's exquisite stereocontrol is due to the preorganization of the active site residues which allows only one specific face of the alkene to approach the reactive C(4a)-hydroperoxyflavin moiety. Furthermore, MonCI has an unusually large substrate-binding cavity that can accommodate premonensin A in an extended or folded conformation which allows any of the three alkenes to be placed next to C(4a)-hydroperoxyflavin. MonCI, with its ability to perform multiple epoxidations on the same substrate in a stereospecific manner, demonstrates the extraordinary versatility of the flavin-dependent monooxygenase family of enzymes.

SQLE Knockdown inhibits bladder cancer progression by regulating the PTEN/AKT/GSK3β signaling pathway through P53

Bladder cancer (BCa) is one of the most common malignancies worldwide. However, the lack of accurate and effective targeted drugs has become a major problem in current clinical treatment of BCa. Studies have demonstrated that squalene epoxidase (SQLE), as a key rate-limiting enzyme in cholesterol biosynthesis, is involved in cancer development. In this study, our analysis of The Cancer Genome Atlas, The Genotype-Tissue Expression, and Gene Expression Omnibus databases showed that SQLE expression was significantly higher in cancer tissues than it was in adjacent normal tissues, and BCa tissues with a high SQLE expression displayed a poor prognosis. We then confirmed this result in qRT-PCR and immunohistochemical staining experiments, and our vitro studies demonstrated that SQLE knockdown inhibited tumor cell proliferation and metastasis through the PTEN/AKT/GSK3β signaling pathway. By means of rescue experiments, we proved that that P53 is a key molecule in SQLE-mediated regulation of the PTEN/AKT/GSK3β signaling pathway. Simultaneously, we verified the above findings through a tumorigenesis experiment in nude mice. In conclusion, our study shows that SQLE promotes BCa growth through the P53/PTEN/AKT/GSK3β axis, which may serve as a therapeutic biological target for BCa.

Mining and modification of Oryza sativa-derived squalene epoxidase for improved β-amyrin production in Saccharomyces cerevisiae

β-Amyrin is a pentacyclic triterpenoid and has anti-viral, anti-bacterial and anti-inflammatory activities. The synthetic pathway of β-amyrin has been analyzed and its heterogeneous synthesis has been achieved in Saccharomyces cerevisiae. Squalene epoxidase (SQE) catalyzes the oxygenation of squalene to form 2,3-oxidosqualene and is rate-limiting in the synthetic pathways of β-amyrin. The endogenous SQE in S. cerevisiae is insufficient for high production of β-amyrin. Herein, eight squalene epoxidases derived from different plants were selected and characterized in S. cerevisiae for improved biosynthesis of β-amyrin. Among them, the squalene epoxidase from Oryza sativa (OsSQE52) showed the best performance compared to other plant-derived sources. Through protein remodeling, the mutant OsSQE52L256R, obtained based on modeling analysis, increased the titer of β-amyrin by 2.43-fold compared to that in the control strain with ERG1 overexpressed under the same conditions. Moreover, the expression of OsSQE52L256R was optimized with the improvement of precursor supply to further increase the production of β-amyrin. Finally, the constructed strains produced 66.97 mg/L β-amyrin in the shake flask, which was 6.45-fold higher than the original strain. Our study provides alternative SQEs for efficient production of β-amyrin as well as other triterpenoids derived from 2,3-oxidosqualene.

Reduced Survival and Resistance of Rhodotorula mucilaginosa Following Inhibition of Pigment Production by Naftifine

Pigments produced by micro-organisms could contribute to their pathogenesis and resistance. The investigation into the red pigment of R. mucilaginosa and its ability to survive and resist has not yet been explored. This study aimed to investigate the survival and resistance of the R. mucilaginosa CQMU1 strain following inhibition of pigment production by naftifine and its underlying mechanism. The red-pigmented Rhodotorula mucilaginosa CQMU1 yeast was isolated from an infected toenail of a patient with onychomycosis. Cultivation of R. mucilaginosa in liquid and solid medium showed the effect of naftifine after treatment. Then, analysis of phagocytosis and tolerance to heat or chemicals of R. mucilaginosa was used to evaluate the survival and resistance of yeast to different treatments. Naftifine reversibly inhibited the pigmentation of R. mucilaginosa CQMU1 in solid and liquid media. Depigmented R. mucilaginosa CQMU1 showed increased susceptibility toward murine macrophage cells RAW264.7 and reduced resistance toward different types of chemicals, such as 1.5-M NaCl and 0.5% Congo red. Inhibition of pigment production by naftifine affected the survival and growth of R. mucilaginosa and its resistance to heat and certain chemicals. The results obtained could further elucidate the target of new mycosis treatment.

Isolation of Terbinafine-Resistant Trichophyton rubrum from Onychomycosis Patients Who Failed Treatment at an Academic Center in New York, United States

Onychomycosis is a common nail infection. Terbinafine-resistant dermatophyte infections pose an emerging global public health concern, but few cases have been described in the United States. We retrospectively reviewed and characterized clinical, histopathological, and mycological features of patients with mycologically confirmed onychomycosis who failed oral terbinafine treatment for onychomycosis at a U.S. academic nail referral center and ascertained for terbinafine-resistant isolates. During 1 June 2022-31 January 2023 at Weill Cornell Medicine in New York City, USA, 96 patients with mycologically confirmed onychomycosis were treated with oral terbinafine. Among 64 patients with adequate follow-up, 36 had clinical or complete cure. Of 28 patients who failed treatment, 17 underwent terbinafine resistance testing. Trichophyton rubrum with terbinafine resistance-conferring mutations was isolated from two patients. Overall, terbinafine failures for onychomycosis were relatively common, with some cases associated with terbinafine-resistant T. rubrum infections. These findings underscore the need for a clinical awareness of this emerging problem and public health efforts to monitor and prevent spread. We highlight the importance of diagnostic testing and species identification for onychomycosis patients and the increasingly important role of fungal identification and susceptibility testing to guide therapy.

Tailoring enzyme strategies and functional groups in biosynthetic pathways

Covering: 2000 to 2022Secondary metabolites are assembled by drawing off and committing some of the flux of primary metabolic building blocks to sets of enzymes that tailor the maturing scaffold to increase architectural and framework complexity, often balancing hydrophilic and hydrophobic surfaces. In this review we examine the small number of chemical strategies that tailoring enzymes employ in maturation of scaffolds. These strategies depend both on the organic functional groups present at each metabolic stage and one of two tailoring enzyme strategies. Nonoxidative tailoring enzymes typically transfer electrophilic fragments, acyl, alkyl and glycosyl groups, from a small set of thermodynamically activated but kinetically stable core metabolites. Oxidative tailoring enzymes can be oxygen-independent or oxygen-dependent. The oxygen independent oxidoreductases are often reversible nicotinamide-utilizing redox catalysts, flipping the nucleophilicity and electrophilicity of functional groups in pathway intermediates. O₂-dependent oxygenases, both mono- and dioxygenases, act by orthogonal, one electron strategies, generating carbon radical species. At sp³ substrate carbons, product alcohols may then behave as nucleophiles for subsequent waves of enzymatic tailoring. At sp² carbons in olefins, electrophilic epoxides have opposite reactivity and often function as "disappearing groups", opened by intramolecular nucleophiles during metabolite maturation. "Thwarted" oxygenases generate radical intermediates that rearrange internally and are not captured oxygenatively.

Hypoxia truncates and constitutively activates the key cholesterol synthesis enzyme squalene monooxygenase

Cholesterol synthesis is both energy- and oxygen-intensive, yet relatively little is known of the regulatory effects of hypoxia on pathway enzymes. We previously showed that the rate-limiting and first oxygen-dependent enzyme of the committed cholesterol synthesis pathway, squalene monooxygenase (SM), can undergo partial proteasomal degradation that renders it constitutively active. Here, we show hypoxia is a physiological trigger for this truncation, which occurs through a two-part mechanism: (1) increased targeting of SM to the proteasome via stabilization of the E3 ubiquitin ligase MARCHF6 and (2) accumulation of the SM substrate, squalene, which impedes the complete degradation of SM and liberates its truncated form. This preserves SM activity and downstream pathway flux during hypoxia. These results uncover a feedforward mechanism that allows SM to accommodate fluctuating substrate levels and may contribute to its widely reported oncogenic properties.

Squalene epoxidase promotes hepatocellular carcinoma development by activating STRAP transcription and TGF-β/SMAD signalling

BACKGROUND AND PURPOSE

Squalene epoxidase (SQLE) is a key enzyme involved in cholesterol biosynthesis, but growing evidence also reveals that SQLE is abnormally expressed in some types of malignant tumours, even though the underlying mechanism remains poorly understood.

EXPERIMENTAL APPROACH

Bioinformatics analysis and RNA sequencing were applied to detect differentially expressed genes in clinical hepatocellular carcinoma (HCC). MTT, colony formation, AnnexinV-FITC/PI, EdU, wound healing, transwell, western blot, qRT-PCR, IHC, F-actin, RNA-sequencing, dual-luciferase reporters, and H&E staining were used to investigate the pharmacological effects and possible mechanisms of SQLE.

KEY RESULTS

SQLE expression was specifically elevated in HCC, correlating with poor clinical outcomes. SQLE significantly promoted HCC growth, epithelial-mesenchymal transition, and metastasis both in vitro and in vivo. RNA sequencing and functional experiments revealed that the protumourigenic effect of SQLE on HCC was closely related to the activation of TGF-β/SMAD signalling, but the stimulatory effect of SQLE on TGF-β/SMAD signalling and HCC development is critically dependent on STRAP. SQLE expression is well correlated with STRAP in HCC, and further, to amplify TGF-β/SMAD signalling, SQLE even transcriptionally increased STRAP gene expression mediated by AP-2α. Finally, as a chemical inhibitor of SQLE, NB-598 markedly inhibited HCC cell growth and tumour development.

CONCLUSIONS AND IMPLICATIONS

Taken together, SQLE serves as a novel oncogene in HCC development by activating TGF-β/SMAD signalling. Targeting SQLE could be useful in drug development and therapy for HCC.

Lipid saturation induces degradation of squalene epoxidase for sterol homeostasis and cell survival

A fluid membrane containing a mix of unsaturated and saturated lipids is essential for life. However, it is unclear how lipid saturation might affect lipid homeostasis, membrane-associated proteins, and membrane organelles. Here, we generate temperature-sensitive mutants of the sole fatty acid desaturase gene OLE1 in the budding yeast Saccharomyces cerevisiae Using these mutants, we show that lipid saturation triggers the endoplasmic reticulum-associated degradation (ERAD) of squalene epoxidase Erg1, a rate-limiting enzyme in sterol biosynthesis, via the E3 ligase Doa10-Ubc7 complex. We identify the P469L mutation that abolishes the lipid saturation-induced ERAD of Erg1. Overexpressed WT or stable Erg1 mutants all mislocalize into foci in the ole1 mutant, whereas the stable Erg1 causes aberrant ER and severely compromises the growth of ole1, which are recapitulated by doa10 deletion. The toxicity of the stable Erg1 and doa10 deletion is due to the accumulation of lanosterol and misfolded proteins in ole1 Our study identifies Erg1 as a novel lipid saturation-regulated ERAD target, manifesting a close link between lipid homeostasis and proteostasis that maintains sterol homeostasis under the lipid saturation condition for cell survival.

Applications of protein engineering in the microbial synthesis of plant triterpenoids

Triterpenoids are a class of natural products widely used in fields related to medicine and health due to their biological activities such as hepatoprotection, anti-inflammation, anti-viral, and anti-tumor. With the advancement in biotechnology, microorganisms have been used as cell factories to produce diverse natural products. Despite the significant progress that has been made in the construction of microbial cell factories for the heterogeneous biosynthesis of triterpenoids, the industrial production of triterpenoids employing microorganisms has been stymied due to the shortage of efficient enzymes as well as the low expression and low catalytic activity of heterologous proteins in microbes. Protein engineering has been demonstrated as an effective way for improving the specificity, catalytic activity, and stability of the enzyme, which can be employed to overcome these challenges. This review summarizes the current progress in the studies of Oxidosqualene cyclases (OSCs), cytochrome P450s (P450s), and UDP-glycosyltransferases (UGTs), the key enzymes in the triterpenoids synthetic pathway. The main obstacles restricting the efficient catalysis of these key enzymes are analyzed, the applications of protein engineering for the three key enzymes in the microbial synthesis of triterpenoids are systematically reviewed, and the challenges and prospects of protein engineering are also discussed.

Targeting the key cholesterol biosynthesis enzyme squalene monooxygenasefor cancer therapy

Cholesterol metabolism is often dysregulated in cancer. Squalene monooxygenase (SQLE) is the second rate-limiting enzyme involved in cholesterol synthesis. Since the discovery of SQLE dysregulation in cancer, compelling evidence has indicated that SQLE plays a vital role in cancer initiation and progression and is a promising therapeutic target for cancer treatment. In this review, we provide an overview of the role and regulation of SQLE in cancer and summarize the updates of antitumor therapy targeting SQLE.

A Structural and Bioinformatics Investigation of a Fungal Squalene Synthase and Comparisons with Other Membrane Proteins

There is interest in the development of drugs to treat fungal infections due to the increasing threat of drug resistance, and here, we report the first crystallographic structure of the catalytic domain of a fungal squalene synthase (SQS), Aspergillus flavus SQS (AfSQS), a potential drug target, together with a bioinformatics study of fungal, human, and protozoal SQSs. Our X-ray results show strong structural similarities between the catalytic domains in these proteins, but, remarkably, using bioinformatics, we find that there is also a large, highly polar helix in the fungal proteins that connects the catalytic and membrane-anchoring transmembrane domains. This polar helix is absent in squalene synthases from all other lifeforms. We show that the transmembrane domain in AfSQS and in other SQSs, stannin, and steryl sulfatase, have very similar properties (% polar residues, hydrophobicity, and hydrophobic moment) to those found in the "penultimate" C-terminal helical domain in squalene epoxidase, while the final C-terminal domain in squalene epoxidase is more polar and may be monotopic. We also propose structural models for full-length AfSQS based on the bioinformatics results as well as a deep learning program that indicate that the C-terminus region may also be membrane surface-associated. Taken together, our results are of general interest given the unique nature of the polar helical domain in fungi that may be involved in protein-protein interactions as well as being a future target for antifungals.

SQLE facilitates the pancreatic cancer progression via the lncRNA-TTN-AS1/miR-133b/SQLE axis

Studies have shown that SQLE is highly expressed in a variety of tumours and promotes tumour progression. However, the role of SQLE in pancreatic cancer (PC) has not been reported. Here, we aim to study the role and molecular mechanism of SQLE in PC. Immunohistochemistry and functional experiments showed that SQLE was highly expressed in PC tissues and promoted the proliferation and invasion of PC cells. Terbinafine, an inhibitor of SQLE, inhibited this effect. In order to further study the upstream mechanism that regulates SQLE, we used bioinformatics technology to lock miR-133b and lncRNA-TTN-AS. In situ hybridization was used to detect the expression of miR-133b and lncRNA-TTN-AS1 in PC tissues. The luciferase reporter gene experiment was used to confirm the binding of miR-133b and lncRNA-TTN-AS1. The results showed that miR-133b was down-regulated in PC tissues and negatively correlated with the expression of SQLE. LncRNA-TTN-AS1 was upregulated in pancreatic cancer tissues and positively correlated with the expression of SQLE. Luciferase gene reporter gene analysis confirmed lncRNA-TTN-AS1 directly binded to miR-133b. Therefore, we propose that targeting the lncRNA-TTN-AS1/miR-133b/SQLE axis is expected to provide new ideas for the clinical treatment of PC patients.

Regulated targeting of the monotopic hairpin membrane protein Erg1 requires the GET pathway

The guided entry of tail-anchored proteins (GET) pathway targets C-terminally anchored transmembrane proteins and protects cells from lipotoxicity. Here, we reveal perturbed ergosterol production in ∆get3 cells and demonstrate the sensitivity of GET pathway mutants to the sterol synthesis inhibiting drug terbinafine. Our data uncover a key enzyme of sterol synthesis, the hairpin membrane protein squalene monooxygenase (Erg1), as a non-canonical GET pathway client, thus rationalizing the lipotoxicity phenotypes of GET pathway mutants. Get3 recognizes the hairpin targeting element of Erg1 via its classical client-binding pocket. Intriguingly, we find that the GET pathway is especially important for the acute upregulation of Erg1 induced by low sterol conditions. We further identify several other proteins anchored to the endoplasmic reticulum (ER) membrane exclusively via a hairpin as putative clients of the GET pathway. Our findings emphasize the necessity of dedicated targeting pathways for high-efficiency targeting of particular clients during dynamic cellular adaptation and highlight hairpin proteins as a potential novel class of GET clients.

Targeting of Mevalonate-Isoprenoid Pathway in Acute Myeloid Leukemia Cells by Bisphosphonate Drugs

Metabolic reprogramming represents a hallmark of tumorigenesis to sustain survival in harsh conditions, rapid growth and metastasis in order to resist to cancer therapies. These metabolic alterations involve glucose metabolism, known as the Warburg effect, increased glutaminolysis and enhanced amino acid and lipid metabolism, especially the cholesterol biosynthesis pathway known as the mevalonate pathway and these are upregulated in several cancer types, including acute myeloid leukemia (AML). In particular, it was demonstrated that the mevalonate pathway has a pivotal role in cellular transformation. Therefore, targeting this biochemical process with drugs such as statins represents a promising therapeutic strategy to be combined with other anticancer treatments. In the last decade, several studies have revealed that amino-bisphosphonates (BP), primarily used for bone fragility disorders, also exhibit potential anti-cancer activity in leukemic cells, as well as in patients with symptomatic multiple myeloma. Indeed, these compounds inhibit the farnesyl pyrophosphate synthase, a key enzyme in the mevalonate pathway, reducing isoprenoid formation of farnesyl pyrophosphate and geranylgeranyl pyrophosphate. This, in turn, inhibits the prenylation of small Guanosine Triphosphate-binding proteins, such as Ras, Rho, Rac, Rab, which are essential for regulating cell survival membrane ruffling and trafficking, interfering with cancer key signaling events involved in clonal expansion and maturation block of progenitor cells in myeloid hematological malignancies. Thus, in this review, we discuss the recent advancements about bisphosphonates’ effects, especially zoledronate, analyzing the biochemical mechanisms and anti-tumor effects on AML model systems. Future studies will be oriented to investigate the clinical relevance and significance of BP treatment in AML, representing an attractive therapeutic strategy that could be integrated into chemotherapy.

2-Aminoselenazoles and 2-aminothiazoles: One-pot synthesis and control of the fungus Colletotrichum lindemuthianum in common beans

BACKGROUND

Anthracnose, caused by the fungus Colletotrichum lindemuthianum, increases losses in the production of common beans. As 1,3-diazoles can act against fungi by inhibiting the enzyme squalene epoxidase (SE), 2-aminoselenazoles and 2-aminothiazoles were synthesized and subjected to tests with the fungus. In addition, the interactions of the most promising substances with the enzyme SE were investigated in silico.

RESULTS

Seventeen compounds (eight new) were prepared by a one-pot methodology. In vitro antifungal activities of these compounds against C. lindemuthianum were determined by the minimum inhibitory concentration (MIC) method. Most treatments differed from the control (water), and six azoles with the lowest MIC values underwent an assay employing common bean plants inoculated with the fungus. Among the best results were those from 2-(3-fluorophenyl)amino-4-phenyl-1,3-thiazole (16; 2857 μg mL^-1 ), which reduced the severity of anthracnose in common beans to values statistically comparable to the commercial fungicide thiophanate-methyl (700 μg mL^-1 ). The in silico affinity of compound 16 for SE was statistically equal to those calculated for several inhibitors of this enzyme.

CONCLUSIONS

The results suggested that 2-(3-fluorophenyl)amino-4-phenyl-1,3-thiazole (16) could be considered a potential fungicidal lead compound for further structural optimization, which according to the in silico study acts via SE inhibition. © 2022 Society of Chemical Industry.

Biosynthetic pathways of triterpenoids and strategies to improve their Biosynthetic Efficiency

"Triterpenoids" can be considered natural products derived from the cyclization of squalene, yielding 3-deoxytriterpenes (hydrocarbons) or 3-hydroxytriterpenes. Triterpenoids are metabolites of these two classes of triterpenes, produced by the functionalization of their carbon skeleton. They can be categorized into different groups based on their structural formula/design. Triterpenoids are an important group of compounds that are widely used in the fields of pharmacology, food, and industrial biotechnology. However, inadequate synthetic methods and insufficient knowledge of the biosynthesis of triterpenoids, such as their structure, enzymatic activity, and the methods used to produce pure and active triterpenoids, are key problems that limit the production of these active metabolites. Here, we summarize the derivatives, pharmaceutical properties, and biosynthetic pathways of triterpenoids and review the enzymes involved in their biosynthetic pathway. Furthermore, we concluded the screening methods, identified the genes involved in the pathways, and highlighted the appropriate strategies used to enhance their biosynthetic production to facilitate the commercial process of triterpenoids through the synthetic biology method.

A three-organelle complex made by wrappER contacts with peroxisomes and mitochondria responds to liver lipid flux changes

Hepatic lipid homeostasis depends on intracellular pathways that respire fatty acid in peroxisomes and mitochondria, and on systemic pathways that secrete fatty acid into the bloodstream, either free or condensed in very-low-density lipoprotein (VLDL) triglycerides. These systemic and intracellular pathways are interdependent, but it is unclear whether and how they integrate into a single cellular circuit. Here, we report that mouse liver wrappER, a distinct endoplasmic reticulum (ER) compartment with apparent fatty acid- and VLDL-secretion functions, connects peroxisomes and mitochondria. Correlative light electron microscopy, quantitative serial section electron tomography and three-dimensional organelle reconstruction analysis show that the number of peroxisome-wrappER-mitochondria complexes changes throughout fasting-to-feeding transitions and doubles when VLDL synthesis stops following acute genetic ablation of Mttp in the liver. Quantitative proteomic analysis of peroxisome-wrappER-mitochondria complex-enriched fractions indicates that the loss of Mttp upregulates global fatty acid β-oxidation, thereby integrating the dynamics of this three-organelle association into hepatic fatty acid flux responses. Therefore, liver lipid homeostasis occurs through the convergence of systemic and intracellular fatty acid-elimination pathways in the peroxisome-wrappER-mitochondria complex.