A DNA damage-amplifying nanoagent for cancer treatment via two-way regulation of redox dyshomeostasis and downregulation of tetrahydrofolate.

DNA damage-based therapy is widely used in cancer treatment, yet its therapeutic efficacy is constrained by the redox homeostasis and DNA damage repair mechanisms of tumor cells. To address these limitations and enhance the efficacy of DNA damage-based therapy, HA-CuH@MTX, a copper-histidine metal-organic complex (CuH) loaded with methotrexate (MTX) and modified with hyaluronic acid (HA), was developed to amplify the DNA damage induced. In vitro experiments demonstrated that the presence of both Cu+ and Cu2+ in HA-CuH@MTX enables two-way regulated redox dyshomeostasis (RDH), achieved through Cu+-catalyzed generation of •OH and Cu2+-mediated consumption of glutathione, thereby facilitating efficient DNA oxidative damage. In addition, DNA damage repair is synergistically inhibited by impairing nucleotide synthesis via histidine metabolism and MTX downregulation of tetrahydrofolate, a crucial raw material in nucleotide synthesis. In vivo experiments with 4T1 tumor-bearing mice demonstrate 83.6 % inhibition of tumor growth by HA-CuH@MTX. This work provides a new strategy to amplify the DNA damage caused by DNA damage-based cancer therapies, and holds great potential for improving their therapeutic efficacy.

In vivo determination of the bioavailability of folic acid through the utilization of the PBPK model in conjunction with UPLC.

This paper employed a physiologically based pharmacokinetic model (PBPK) to investigate the transformations of folic acid and its metabolites in vivo. Additionally, an ultra-performance liquid chromatography (UPLC) method was developed to accurately measure the body's retention rate and conversion rate of folic acid, tetrahydrofolate, and 5-methyltetrahydrofolate. Furthermore, the bioavailability of folic acid in the body was assessed by combining this method with an evaluation technique for animal models. The study found that the gastric metabolism time was 2 h, while the small intestinal metabolism duration was 4 h. The maximum conversion rate was observed in plasma and liver after 6 h, and in the brain after 8 h. This serves as a framework for creating a model to assess the bioavailability of folic acid in living organisms, to enhance the safety and efficacy of folic acid intake.

Dysregulation of hepatic one-carbon metabolism in classical homocystinuria: Implications of redox-sensitive DHFR repression and tetrahydrofolate depletion for pathogenesis and treatment.

Cystathionine beta-synthase-deficient homocystinuria (HCU) is a life-threatening disorder of sulfur metabolism. HCU can be treated by using betaine to lower tissue and plasma levels of homocysteine (Hcy). Here, we show that mice with severely elevated Hcy and potentially deficient in the folate species tetrahydrofolate (THF) exhibit a very limited response to betaine indicating that THF plays a critical role in treatment efficacy. Analysis of a mouse model of HCU revealed a 10-fold increase in hepatic levels of 5-methyl -THF and a 30-fold accumulation of formiminoglutamic acid, consistent with a paucity of THF. Neither of these metabolite accumulations were reversed or ameliorated by betaine treatment. Hepatic expression of the THF-generating enzyme dihydrofolate reductase (DHFR) was significantly repressed in HCU mice and expression was not increased by betaine treatment but appears to be sensitive to cellular redox status. Expression of the DHFR reaction partner thymidylate synthase was also repressed and metabolomic analysis detected widespread alteration of hepatic histidine and glutamine metabolism. Many individuals with HCU exhibit endothelial dysfunction. DHFR plays a key role in nitric oxide (NO) generation due to its role in regenerating oxidized tetrahydrobiopterin, and we observed a significant decrease in plasma NOx (NO2 + NO3) levels in HCU mice. Additional impairment of NO generation may also come from the HCU-mediated induction of the 20-hydroxyeicosatetraenoic acid generating cytochrome CYP4A. Collectively, our data shows that HCU induces dysfunctional one-carbon metabolism with the potential to both impair betaine treatment and contribute to multiple aspects of pathogenesis in this disease.

Formate-tetrahydrofolate ligase: supplying the cytosolic one-carbon network in roots with one-carbon units originating from glycolate.

The metabolism of tetrahydrofolate (H4PteGlun)-bound one-carbon (C1) units (C1 metabolism) is multifaceted and required for plant growth, but it is unclear what of many possible synthesis pathways provide C1 units in specific organelles and tissues. One possible source of C1 units is via formate-tetrahydrofolate ligase, which catalyzes the reversible ATP-driven production of 10-formyltetrahydrofolate (10-formyl-H4PteGlun) from formate and tetrahydrofolate (H4PteGlun). Here, we report biochemical and functional characterization of the enzyme from Arabidopsis thaliana (AtFTHFL). We show that the recombinant AtFTHFL has lower Km and kcat values with pentaglutamyl tetrahydrofolate (H4PteGlu5) as compared to monoglutamyl tetrahydrofolate (H4PteGlu1), resulting in virtually identical catalytic efficiencies for the two substrates. Stable transformation of Arabidopsis plants with the EGFP-tagged AtFTHFL, followed with fluorescence microscopy, demonstrated cytosolic signal. Two independent T-DNA insertion lines with impaired AtFTHFL function had shorter roots compared to the wild type plants, demonstrating the importance of this enzyme for root growth. Overexpressing AtFTHFL led to the accumulation of H4PteGlun + 5,10-methylene-H4PteGlun and serine, accompanied with the depletion of formate and glycolate, in roots of the transgenic Arabidopsis plants. This metabolic adjustment supports the hypothesis that AtFTHFL feeds the cytosolic C1 network in roots with C1 units originating from glycolate, and that these units are then used mainly for biosynthesis of serine, and not as much for the biosynthesis of 5-methyl-H4PteGlun, methionine, and S-adenosylmethionine. This finding has implications for any future attempts to engineer one-carbon unit-requiring products through manipulation of the one-carbon metabolic network in non-photosynthetic organs.

Novel Role of 5-Methyl-(6S)-Tetrahydrofolate in Mediating Endothelial Cell Tetrahydrobiopterin in Pregnancy and Implications for Gestational Hypertension.

BACKGROUND: Folate intake during pregnancy is essential for fetal development and maternal health. However, the specific effects of folic acid (FA) and 5-methyl-(6S)-tetrahydrofolate (5-MTHF) on the prevention and treatment of hypertensive disorders of pregnancy remain unclear. We investigated whether FA and 5-MTHF have different effects on endothelial cell tetrahydrobiopterin (BH4) metabolism in pregnancy and the possible consequences for endothelial NO generation, maternal blood pressure, and fetal growth. METHODS: We analyzed the maternal blood pressure in pregnant wild-type (Gch1fl/fl) and Gch1fl/fl Tie2cre mice treated with either FA or 5-MTHF starting before pregnancy, mid-pregnancy or late pregnancy. BH4, superoxide, and NO bioavailability were determined in mouse and human models of endothelial cell BH4 deficiency by high-performance liquid chromatography. RESULTS: In vitro studies in mouse and human endothelial cells showed that treatment with 5-MTHF, but not FA, elevated BH4 levels, reduced superoxide production, and increased NO synthase activity. In primary endothelial cells isolated from women with hypertensive pregnancies, exposure to 5-MTHF, but not FA, restored the reduction in BH4 levels and NO synthase activity. In vivo studies in mice revealed that oral treatment with 5-MTHF, but not FA, prevented and treated hypertension in pregnancy when administered either before or during pregnancy, respectively, and normalized placental and fetal growth restriction if administered from mid-gestation onward. CONCLUSIONS: Collectively, these studies identify a critical role for 5-MTHF in endothelial cell function in pregnancy, related to endothelial cell BH4 availability and NO synthase activity. Thus, 5-MTHF represents a novel therapeutic agent that may potentially improve endothelial function in hypertensive disorders of pregnancy by targeting endothelial cell BH4.

Is there a multidisciplinary role for 5-methyltetrahydrofolate? The obstetric evidence in perspective.

5-methyltetrahydrofolate (5-MTHF), or its synthetic precursor, folic acid, is traditionally used as a supplement for improving fertility and for the prevention of embryonal neural tube defects. However, in the last decade, starting from the effectiveness of this preventive treatment in the gynecological setting, the use of 5-MTHF was extended to other medical and pathological areas. Thus, there might be a rationale for the use of 5-MTHF for purposes other than the protection of the growing embryo linked to the possible effect of MTHFR variants in different pathological conditions. A narrative review was conducted to provide an overview of the available evidence on the use of 5-MTHF in the obstetric field and to critically discuss the available data regarding the use of 5-MTHF across other different therapeutic areas. Results showed that the use of 5-MTHF in pregnancy presents some advantages if compared with folic acid, such as immediate action, the non-necessity of metabolic activation, and the immediate bioavailability of the mother and fetus. Otherwise, the role of 5-MTHF in the management of cardiovascular risk is still debated due to the multiple confounding factors that characterize this patient setting. A link between folate deficiency in pregnancy and postpartum depression has been proposed, as well as between folate levels and the onset of depression. In conclusion, evidence from the literature supports the additional role of 5-MTHF as a pleiotropic drug with a transversal effect in different therapeutic contexts. With regard to the prevention of cardiovascular disorders, available evidence is not conclusive.

Structure-based characterization and compound identification of the wild-type THF class-II riboswitch.

Riboswitches are conserved regulatory RNA elements participating in various metabolic pathways. Recently, a novel RNA motif known as the folE RNA motif was discovered upstream of folE genes. It specifically senses tetrahydrofolate (THF) and is therefore termed THF-II riboswitch. To unravel the ligand recognition mechanism of this newly discovered riboswitch and decipher the underlying principles governing its tertiary folding, we determined both the free-form and bound-form THF-II riboswitch in the wild-type sequences. Combining structural information and isothermal titration calorimetry (ITC) binding assays on structure-based mutants, we successfully elucidated the significant long-range interactions governing the function of THF-II riboswitch and identified additional compounds, including alternative natural metabolites and potential lead compounds for drug discovery, that interact with THF-II riboswitch. Our structural research on the ligand recognition mechanism of the THF-II riboswitch not only paves the way for identification of compounds targeting riboswitches, but also facilitates the exploration of THF analogs in diverse biological contexts or for therapeutic applications.

Tetrahydrofolate levels influence 2-aminoacrylate stress in Salmonella enterica.

In Salmonella enterica, the absence of the RidA deaminase results in the accumulation of the reactive enamine 2-aminoacrylate (2AA). The resulting 2AA stress impacts metabolism and prevents growth in some conditions by inactivating a specific target pyridoxal 5'-phosphate (PLP)-dependent enzyme(s). The detrimental effects of 2AA stress can be overcome by changing the sensitivity of a critical target enzyme or modifying flux in one or more nodes in the metabolic network. The catabolic L-alanine racemase DadX is a target of 2AA, which explains the inability of an alr ridA strain to use L-alanine as the sole nitrogen source. Spontaneous mutations that suppressed the growth defect of the alr ridA strain were identified as lesions in folE, which encodes GTP cyclohydrolase and catalyzes the first step of tetrahydrofolate (THF) synthesis. The data here show that THF limitation resulting from a folE lesion, or inhibition of dihydrofolate reductase (FolA) by trimethoprim, decreases the 2AA generated from endogenous serine. The data are consistent with an increased level of threonine, resulting from low folate levels, decreasing 2AA stress.IMPORTANCERidA is an enamine deaminase that has been characterized as preventing the 2-aminoacrylate (2AA) stress. In the absence of RidA, 2AA accumulates and damages various cellular enzymes. Much of the work describing the 2AA stress system has depended on the exogenous addition of serine to increase the production of the enamine stressor. The work herein focuses on understanding the effect of 2AA stress generated from endogenous serine pools. As such, this work describes the consequences of a subtle level of stress that nonetheless compromises growth in at least two conditions. Describing mechanisms that alter the physiological consequences of 2AA stress increases our understanding of endogenous metabolic stress and how the robustness of the metabolic network allows perturbations to be modulated.

Engineering Redox Cofactor Balance for Improved 5-Methyltetrahydrofolate Production in Escherichia coli.

5-Methyltetrahydrofolate (5-MTHF) is the sole active form of folate functioning in the human body and is widely used as a nutraceutical. Unlike the pollution from chemical synthesis, microbial synthesis enables green production of 5-MTHF. In this study, Escherichia coli BL21 (DE3) was selected as the host. Initially, by deleting 6-phosphofructokinase 1 and overexpressing glucose-6-phosphate 1-dehydrogenase and 6-phosphogluconate dehydrogenase, the glycolysis pathway flux decreased, while the pentose phosphate pathway flux enhanced. The ratios of NADH/NAD+ and NADPH/NADP+ increased, indicating elevated NAD(P)H supply. This led to more folate being reduced and the successful accumulation of 5-MTHF to 44.57 µg/L. Subsequently, formate dehydrogenases from Candida boidinii and Candida dubliniensis were expressed, which were capable of catalyzing the reaction of sodium formate oxidation for NAD(P)H regeneration. This further increased the NAD(P)H supply, leading to a rise in 5-MTHF production to 247.36 µg/L. Moreover, to maintain the balance between NADH and NADPH, pntAB and sthA, encoding transhydrogenase, were overexpressed. Finally, by overexpressing six key enzymes in the folate to 5-MTHF pathway and employing fed-batch cultivation in a 3 L fermenter, strain Z13 attained a peak 5-MTHF titer of 3009.03 µg/L, the highest level reported in E. coli so far. This research is a significant step toward industrial-scale microbial 5-MTHF production.

The role of methionine synthases in fungal metabolism and virulence.

Methionine synthases (MetH) catalyse the methylation of homocysteine (Hcy) with 5-methyl-tetrahydrofolate (5, methyl-THF) acting as methyl donor, to form methionine (Met) and tetrahydrofolate (THF). This function is performed by two unrelated classes of enzymes that differ significantly in both their structures and mechanisms of action. The genomes of plants and many fungi exclusively encode cobalamin-independent enzymes (EC.2.1.1.14), while some fungi also possess proteins from the cobalamin-dependent (EC.2.1.1.13) family utilised by humans. Methionine synthase's function connects the methionine and folate cycles, making it a crucial node in primary metabolism, with impacts on important cellular processes such as anabolism, growth and synthesis of proteins, polyamines, nucleotides and lipids. As a result, MetHs are vital for the viability or virulence of numerous prominent human and plant pathogenic fungi and have been proposed as promising broad-spectrum antifungal drug targets. This review provides a summary of the relevance of methionine synthases to fungal metabolism, their potential as antifungal drug targets and insights into the structures of both classes of MetH.

Tailored extraction and ion mobility-mass spectrometry enables isotopologue analysis of tetrahydrofolate vitamers.

Climate change directs the focus in biotechnology increasingly on one-carbon metabolism for fixation of CO2 and CO2-derived chemicals (e.g. methanol, formate) to reduce our reliance on both fossil and food-competing carbon sources. The tetrahydrofolate pathway is involved in several one-carbon fixation pathways. To study such pathways, stable isotope-labelled tracer analysis performed with mass spectrometry is state of the art. However, no such method is currently available for tetrahydrofolate vitamers. In the present work, we established a fit-for-purpose extraction method for the methylotrophic yeast Komagataella phaffii that allows access to intracellular methyl- and methenyl-tetrahydrofolate (THF) with demonstrated stability over several hours. To determine isotopologue distributions of methyl-THF, LC-QTOFMS provides a selective fragment ion with suitable intensity of at least two isotopologues in all samples, but not for methenyl-THF. However, the addition of ion mobility separation provided a critical selectivity improvement allowing accurate isotopologue distribution analysis of methenyl-THF with LC-IM-TOFMS. Application of these new methods for 13C-tracer experiments revealed a decrease from 83 ± 4 to 64 ± 5% in the M + 0 carbon isotopologue fraction in methyl-THF after 1 h of labelling with formate, and to 54 ± 5% with methanol. The M + 0 carbon isotopologue fraction of methenyl-THF was reduced from 83 ± 2 to 78 ± 1% over the same time when using 13C-methanol labelling. The labelling results of multiple strains evidenced the involvement of the THF pathway in the oxygen-tolerant reductive glycine pathway, the presence of the in vivo reduction of formate to formaldehyde, and the activity of the spontaneous condensation reaction of formaldehyde with THF in K. phaffii.

A new metabolic trait in an acetogen: Mixed acid fermentation of fructose in a methylene-tetrahydrofolate reductase mutant of Acetobacterium woodii.

To inactivate the Wood-Ljungdahl pathway in the acetogenic model bacterium Acetobacterium woodii, the genes metVF encoding two of the subunits of the methylene-tetrahydrofolate reductase were deleted. As expected, the mutant did not grow on C1 compounds and also not on lactate, ethanol or butanediol. In contrast to a mutant in which the first enzyme of the pathway (hydrogen-dependent CO2 reductase) had been genetically deleted, cells were able to grow on fructose, albeit with lower rates and yields than the wild-type. Growth was restored by addition of an external electron sink, glycine betaine + CO2 or caffeate. Resting cells pre-grown on fructose plus an external electron acceptor fermented fructose to two acetate and four hydrogen, that is, performed hydrogenogenesis. Cells pre-grown under fermentative conditions on fructose alone redirected carbon and electrons to form lactate, formate, ethanol as well as hydrogen. Apparently, growth on fructose alone induced enzymes for mixed acid fermentation (MAF). Transcriptome analyses revealed enzymes potentially involved in MAF and a quantitative model for MAF from fructose in A. woodii is presented.

Structural insights into translation regulation by the THF-II riboswitch.

In bacteria, expression of folate-related genes is controlled by the tetrahydrofolate (THF) riboswitch in response to specific binding of THF and its derivatives. Recently, a second class of THF riboswitches, named THF-II, was identified in Gram-negative bacteria, which exhibit distinct architecture from the previously characterized THF-I riboswitches found in Gram-positive bacteria. Here, we present the crystal structures of the ligand-bound THF-II riboswitch from Mesorhizobium loti. These structures exhibit a long rod-like fold stabilized by continuous base pair and base triplet stacking across two helices of P1 and P2 and their interconnecting ligand-bound binding pocket. The pterin moiety of the ligand docks into the binding pocket by forming hydrogen bonds with two highly conserved pyrimidines in J12 and J21, which resembles the hydrogen-bonding pattern at the ligand-binding site FAPK in the THF-I riboswitch. Using small-angle X-ray scattering and isothermal titration calorimetry, we further characterized the riboswitch in solution and reveal that Mg2+ is essential for pre-organization of the binding pocket for efficient ligand binding. RNase H cleavage assay indicates that ligand binding reduces accessibility of the ribosome binding site in the right arm of P1, thus down-regulating the expression of downstream genes. Together, these results provide mechanistic insights into translation regulation by the THF-II riboswitch.

Proteomic, Transcriptomic, Mutational, and Functional Assays Reveal the Involvement of Both THF and PLP Sites at the GmSHMT08 in Resistance to Soybean Cyst Nematode.

The serine hydroxymethyltransferase (SHMT; E.C. 2.1.2.1) is involved in the interconversion of serine/glycine and tetrahydrofolate (THF)/5,10-methylene THF, playing a key role in one-carbon metabolism, the de novo purine pathway, cellular methylation reactions, redox homeostasis maintenance, and methionine and thymidylate synthesis. GmSHMT08 is the soybean gene underlying soybean cyst nematode (SCN) resistance at the Rhg4 locus. GmSHMT08 protein contains four tetrahydrofolate (THF) cofactor binding sites (L129, L135, F284, N374) and six pyridoxal phosphate (PLP) cofactor binding/catalysis sites (Y59, G106, G107, H134, S190A, H218). In the current study, proteomic analysis of a data set of protein complex immunoprecipitated using GmSHMT08 antibodies under SCN infected soybean roots reveals the presence of enriched pathways that mainly use glycine/serine as a substrate (glyoxylate cycle, redox homeostasis, glycolysis, and heme biosynthesis). Root and leaf transcriptomic analysis of differentially expressed genes under SCN infection supported the proteomic data, pointing directly to the involvement of the interconversion reaction carried out by the serine hydroxymethyltransferase enzyme. Direct site mutagenesis revealed that all mutated THF and PLP sites at the GmSHMT08 resulted in increased SCN resistance. We have shown the involvement of PLP sites in SCN resistance. Specially, the effect of the two Y59 and S190 PLP sites was more drastic than the tested THF sites. This unprecedented finding will help us to identify the biological outcomes of THF and PLP residues at the GmSHMT08 and to understand SCN resistance mechanisms.

Isoquercitrin from Apocynum venetum L. produces an anti-obesity effect on obese mice by targeting C-1-tetrahydrofolate synthase, carbonyl reductase, and glutathione S-transferase P and modification of the AMPK/SREBP-1c/FAS/CD36 signaling pathway in mice in vivo.

In the present study, mice with high-fat-diet-induced obesity were used in investigating the anti-obesity effects of an aqueous extract and isoquercitrin from Apocynum venetum L. The aqueous extract and the signal molecule isoquercitrin significantly reduced the body weight gain, food intake, water consumption, and fasting blood glucose, plasma triglyceride and total cholesterol levels of the obese mice. Furthermore, the mechanism of action of isoquercitrin was explored through RT-PCR analyses and uptake experiments of adenosine 5'-monophosphate-activated protein kinase (AMPK) and sterol regulatory-element binding protein (SREBP-1c) inhibitors and glucose. The indexes of SREBP-1c, fatty acid synthase (FAS), stearoyl-CoA desaturase-1 (SCD), and cluster of differentiation 36 (CD36) in obese mice significantly increased but returned to normal levels after the administration of isoquercitrin. Meanwhile, the anti-obesity effect of isoquercitrin was diminished by the inhibitors of AMPK and SREBP-1c. In addition, intestinal glucose uptake in normal mice was significantly inhibited after the oral administration of isoquercitrin. Moreover, 2D gel electrophoresis based proteome-wide cellular thermal shift assay (CETSA) showed that the potential target proteins of isoquercitrin were C-1-tetrahydrofolate synthase, carbonyl reductase, and glutathione S-transferase P. These results suggested that isoquercitrin produces an anti-obesity effect by targeting the above-mentioned proteins and regulating the AMPK/SREBP-1c signaling pathway and potentially prevents obesity and obesity-related metabolic disorders.

Biosynthesis of L-5-methyltetrahydrofolate by genetically engineered Escherichia coli.

L-5-Methyltetrahydrofolate (L-5-MTHF) is the only biologically active form of folate in the human body. Production of L-5-MTHF by using microbes is an emerging consideration for green synthesis. However, microbes naturally produce only a small amount of L-5-MTHF. Here, Escherichia coli BL21(DE3) was engineered to increase the production of L-5-MTHF by overexpressing the intrinsic genes of dihydrofolate reductase and methylenetetrahydrofolate (methylene-THF) reductase, introducing the genes encoding formate-THF ligase, formyl-THF cyclohydrolase and methylene-THF dehydrogenase from the one-carbon metabolic pathway of Methylobacterium extorquens or Clostridium autoethanogenum and disrupting the gene of methionine synthase involved in the consumption and synthesis inhibition of the target product. Thus, upon its native pathway, an additional pathway for L-5-MTHF synthesis was developed in E. coli, which was further analysed and confirmed by qRT-PCR, enzyme assays and metabolite determination. After optimizing the conditions of induction time, temperature, cell density and concentration of IPTG and supplementing exogenous substances (folic acid, sodium formate and glucose) to the culture, the highest yield of 527.84 µg g-1 of dry cell weight for L-5-MTHF was obtained, which was about 11.8 folds of that of the original strain. This study paves the way for further metabolic engineering to improve the biosynthesis of L-5-MTHF in E. coli.

The iron-sulfur cluster assembly (ISC) protein Iba57 executes a tetrahydrofolate-independent function in mitochondrial [4Fe-4S] protein maturation.

Mitochondria harbor the bacteria-inherited iron-sulfur cluster assembly (ISC) machinery to generate [2Fe-2S; iron-sulfur (Fe-S)] and [4Fe-4S] proteins. In yeast, assembly of [4Fe-4S] proteins specifically involves the ISC proteins Isa1, Isa2, Iba57, Bol3, and Nfu1. Functional defects in their human equivalents cause the multiple mitochondrial dysfunction syndromes, severe disorders with a broad clinical spectrum. The bacterial Iba57 ancestor YgfZ was described to require tetrahydrofolate (THF) for its function in the maturation of selected [4Fe-4S] proteins. Both YgfZ and Iba57 are structurally related to an enzyme family catalyzing THF-dependent one-carbon transfer reactions including GcvT of the glycine cleavage system. On this basis, a universally conserved folate requirement in ISC-dependent [4Fe-4S] protein biogenesis was proposed. To test this idea for mitochondrial Iba57, we performed genetic and biochemical studies in Saccharomyces cerevisiae, and we solved the crystal structure of Iba57 from the thermophilic fungus Chaetomium thermophilum. We provide three lines of evidence for the THF independence of the Iba57-catalyzed [4Fe-4S] protein assembly pathway. First, yeast mutants lacking folate show no defect in mitochondrial [4Fe-4S] protein maturation. Second, the 3D structure of Iba57 lacks many of the side-chain contacts to THF as defined in GcvT, and the THF-binding pocket is constricted. Third, mutations in conserved Iba57 residues that are essential for THF-dependent catalysis in GcvT do not impair Iba57 function in vivo, in contrast to an exchange of the invariant, surface-exposed cysteine residue. We conclude that mitochondrial Iba57, despite structural similarities to both YgfZ and THF-binding proteins, does not utilize folate for its function.

Effect of germination on the main chemical compounds and 5-methyltetrahydrofolate metabolism of different quinoa varieties.

This study determined the content of macronutrients and micronutrients to investigate the nutritional value and health benefits of six varieties of quinoa seeds and sprouts. Germination markedly increased the contents of proteins, reducing sugars, free amino acids, vitamins, and phytochemicals such as phenolic and carotenoid compounds, with variation among different quinoa varieties. Relatively high levels of 5-methyltetrahydrofolate (5-MTHF) were found in 6-day-old quinoa sprouts, especially in the LL-1 variety (1747.25 µg/100 g DW), followed by QL-2 sprouts (1501.67 µg/100 g DW). Furthermore, we examined the relative expression of genes involved in the folate biosynthetic pathway during QL-2 germination. The expression of the ADCS gene was upregulated 28.31-fold in 6-day-old sprouts, greatly facilitating folate synthesis. Pterin synthesis genes regulate the biosynthesis and further accumulation of folate by controlling pterin metabolic flux. Overall, the 6-day-old sprouts were recommended as a functional food with nutritional value and health benefits in dietary supplements.

The Second Class of Tetrahydrofolate (THF-II) Riboswitches Recognizes the Tetrahydrofolic Acid Ligand via Local Conformation Changes.

Riboswitches are regulatory noncoding RNAs found in bacteria, fungi and plants, that modulate gene expressions through structural changes in response to ligand binding. Understanding how ligands interact with riboswitches in solution can shed light on the molecular mechanisms of this ancient regulators. Previous studies showed that riboswitches undergo global conformation changes in response to ligand binding to relay information. Here, we report conformation switching models of the recently discovered tetrahydrofolic acid-responsive second class of tetrahydrofolate (THF-II) riboswitches in response to ligand binding. Using a combination of selective 2'-hydroxyl acylation, analyzed by primer extension (SHAPE) assay, 3D modeling and small-angle X-ray scattering (SAXS), we found that the ligand specifically recognizes and reshapes the THF-II riboswitch loop regions, but does not affect the stability of the P3 helix. Our results show that the THF-II riboswitch undergoes only local conformation changes in response to ligand binding, rearranging the Loop1-P3-Loop2 region and rotating Loop1 from a ~120° angle to a ~75° angle. This distinct conformation changes suggest a unique regulatory mechanism of the THF-II riboswitch, previously unseen in other riboswitches. Our findings may contribute to the fields of RNA sensors and drug design.

Absorption and Tissue Distribution of Folate Forms in Rats: Indications for Specific Folate Form Supplementation during Pregnancy.

Food fortification and folic acid supplementation during pregnancy have been implemented as strategies to prevent fetal malformations during pregnancy. However, with the emergence of conditions where folate metabolism and transport are disrupted, such as folate receptor alpha autoantibody (FRαAb)-induced folate deficiency, it is critical to find a folate form that is effective and safe for pharmacologic dosing for prolonged periods. Therefore, in this study, we explored the absorption and tissue distribution of folic acid (PGA), 5-methyl-tetrahydrofolate (MTHF), l-folinic acid (levofolinate), and d,l-folinic acid (Leucovorin) in adult rats. During absorption, all forms are converted to MTHF while some unconverted folate form is transported into the blood, especially PGA. The study confirms the rapid distribution of absorbed folate to the placenta and fetus. FRαAb administered, also accumulates rapidly in the placenta and blocks folate transport to the fetus and high folate concentrations are needed to circumvent or overcome the blocking of FRα. In the presence of FRαAb, both Leucovorin and levofolinate are absorbed and distributed to tissues better than the other forms. However, only 50% of the leucovorin is metabolically active whereas levofolinate is fully active and generates higher tetrahydrofolate (THF). Because levofolinate can readily incorporate into the folate cycle without needing methylenetetrahydrofolate reductase (MTHFR) and methionine synthase (MS) in the first pass and is relatively stable, it should be the folate form of choice during pregnancy, other disorders where large daily doses of folate are needed, and food fortification.