Utilisation of 10-formyldihydrofolate as substrate by dihydrofolate reductase (DHFR) and 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) tranformylase/IMP cyclohydrolase (PurH) in Escherichia coli

Identification of a Potential Antimycobacterial Drug Sensitizer Targeting a Flavin-Independent Methylenetetrahydrofolate Reductase

The increasing antibiotic resistance of Mycobacterium tuberculosis and pathogenic nontuberculosis mycobacteria highlights the urgent need for new prevention and treatment strategies. Recently, the cocrystal structure of a Mycobacterium smegmatis flavin-independent 5,10-methylenetetrahydrofolate reductase (MsmMTHFR) that binds with a reduced nicotinamide adenine dinucleotide (NADH) has been well-determined, providing a structural basis for the screening of antimycobacterial leads targeting MsmMTHFR, a new enzyme involved in tetrahydrofolic acid (THF) biosynthesis. In this study, we identified compound AB131 as a promising candidate that fits well into the NADH binding pocket of MsmMTHFR through virtual screening. We discovered that AB131 and its derivatives (13 and 14) can sensitize the antimycobacterial activity of the antitubercular drug para-aminosalicyclic acid (PAS) by 2-5-fold against various species of mycobacteria. Although the compounds themselves do not exhibit any antimycobacterial activity, the high binding affinity of AB131 with MsmMTHFR or Rv2172c was evaluated by microscale thermophoresis analysis. Additionally, we predicted and validated the key residues (V115, V117, P118, and R163) of MsmMTHFR that are involved in the interaction with AB131 by using molecular docking and mutagenesis analysis. These findings offer a potential exploitable target for developing potent and specific antimycobacterial drug sensitizers.

Methionyl-tRNA formyltransferase utilizes 10-formyldihydrofolate as an alternative substrate and impacts antifolate drug action

Methionyl-tRNA formyltransferase (Fmt)-mediated formylation of Met-tRNA^fMet to fMet-tRNA^fMet is crucial for efficient initiation of translation in bacteria and the eukaryotic organelles. Folate dehydrogenase-cyclohydrolase (FolD), a bifunctional enzyme, carries out conversion of 5,10-methylene tetrahydrofolate (5,10-CH₂-THF) to 10-formyl-THF (10-CHO-THF), a metabolite utilized by Fmt as a formyl group donor. In this study, using in vivo and in vitro approaches, we show that 10-CHO-DHF may also be utilized by Fmt as an alternative substrate (formyl group donor) to formylate Met-tRNA^fMet. Dihydrofolate (DHF) formed as a by-product in the in vitro assay was verified by LC-MS/MS analysis. FolD-deficient mutants and Fmt over-expressing strains were more sensitive to trimethoprim (TMP) than the ∆fmt strain, suggesting that the domino effect of TMP leads to inhibition of protein synthesis and strain growth. Antifolate treatment to Escherichia coli showed a decrease in the reduced folate species (THF, 5,10-CH₂-THF, 5-CH₃-THF, 5,10-CH⁺-THF and 5-CHO-THF) and increase in the oxidized folate species (folic acid and DHF). In cells, 10-CHO-DHF and 10-CHO-folic acid were enriched in the stationary phase. This suggests that 10-CHO-DHF is a bioactive metabolite in the folate pathway for generating other folate intermediates and fMet-tRNA^fMet.

Folate metabolic profiling and expression of folate metabolism-related genes during panicle development in foxtail millet (Setaria italica (L.) P. Beauv)

BACKGROUND

Foxtail millet grain has higher folate content than other cereal crops. However, the folate metabolite content and the expression patterns of folate metabolite-related genes are unknown.

RESULTS

Liquid chromatography-mass spectrometry was used to investigate 12 folate metabolites in a foxtail millet panicle. The content of total folate and derivatives gradually decreased during panicle development. Polyglutamate 5-formyl-tetrahydrofolate was the major form. Twenty-eight genes involved in the folate metabolic pathway were identified through bioinformatic analysis. These genes in Setaria italica, S. viridis and Zea mays showed genomic collinearity. Phylogenetic analysis revealed that the folate-related genes were closely related among the C4 plants compared to C3 plants. The gene expressions were then studied at three panicle development stages. The gene expression patterns were classified into two groups, namely SiADCL1 and SiGGH as two key enzymes, which are responsible for folate synthesis and degradation; their expression levels were highest at the early panicle development stage, up to 179.11- and 163.88-fold, respectively. Their expression levels had a similar downward trend during panicle development and were significantly positively correlated with the concentration of total folate and folate derivatives. However, SiSHMT3 expression levels were significantly negatively correlated with total folate concentration.

CONCLUSION

Besides being the major determinants of folate and folate derivatives accumulation, SiADCL1 and SiGGH expression levels are key limiting factors in the foxtail millet panicle. Therefore, SiADCL1 and SiGGH expression levels can be targeted in genetic modification studies to improve folate content in foxtail millet seeds in the future. © 2021 Society of Chemical Industry.

Effects of Sevoflurane Inhalation Anesthesia on the Intestinal Microbiome in Mice

In recent years, more and more attention has been paid to intestinal microbiome. Almost all operations will go through the anesthesia process, but it is not clear whether the intervention of anesthesia alone will affect the change in the intestinal microbiome. The purpose of this study was to verify the effect of sevoflurane inhalation anesthesia on the intestinal microbiome. The animal in the experimental group was used to provide sevoflurane inhalation anesthesia for 4 hours. The control group was not intervened. The feces of the experimental group and the control group were collected on the 1st, 3rd, 7th and 14th days after anesthesia. Sevoflurane inhalation anesthesia will cause changes in the intestinal microbiome of mice. It appears on the 1st day after anesthesia and is most obvious on the 7th day. The specific manifestation is that the abundance of microbiome and the diversity of the microbiome is reduced. At the same time, Untargeted metabonomics showed that compared with the control group, the experimental group had more increased metabolites related to the different microbiome, among which 5-methylthioadenosine was related to the central nervous system. Subsequently, the intestinal microbiome diversity of mice showed a trend of recovery on the 14th day. At the genus level, the fecal samples obtained on the 14th day after anesthesia exhibited significantly increased abundances of Bacteroides, Alloprevotella, and Akkermansia and significantly decreased abundances of Lactobacillus compared with the samples obtained on the 1st day after anesthesia. However, the abundance of differential bacteria did not recover with the changing trend of diversity. Therefore, we believe that sevoflurane inhalation anesthesia is associated with changes in the internal microbiome and metabolites, and this change may be completed through the brain-gut axis, while sevoflurane inhalation anesthesia may change the intestinal microbiome for as long as 14 days or longer.

Monomeric NADH-Oxidizing Methylenetetrahydrofolate Reductases from Mycobacterium smegmatis Lack Flavin Coenzyme

5,10-Methylenetetrahydrofolate reductase (MetF/MTHFR) is an essential enzyme in one-carbon metabolism for de novo biosynthesis of methionine. Our in vivo and in vitro analyses of MSMEG_6664/MSMEI_6484, annotated as putative MTHFR in Mycobacterium smegmatis, failed to reveal their function as MTHFRs. However, we identified two hypothetical proteins, MSMEG_6596 and MSMEG_6649, as noncanonical MTHFRs in the bacterium. MTHFRs are known to be oligomeric flavoproteins. Both MSMEG_6596 and MSMEG_6649 are monomeric proteins and lack flavin coenzymes. In vitro, the catalytic efficiency (k _cat/K_m ) of MSMEG_6596 (MTHFR1) for 5,10-CH₂-THF and NADH was ∼13.5- and 15.3-fold higher than that of MSMEG_6649 (MTHFR2). Thus, MSMEG_6596 is the major MTHFR. This interpretation was further supported by better rescue of the E. coli Δmthfr strain by MTHFR1 than by MTHFR2. As identified by liquid chromatography-tandem mass spectrometry, the product of MTHFR1- or MTHFR2-catalyzed reactions was 5-CH₃-THF. The M. smegmatis Δmsmeg_6596 strain was partially auxotrophic for methionine and grew only poorly without methionine or without being complemented with a functional copy of MTHFR1 or MTHFR2. Furthermore, the Δmsmeg_6596 strain was more sensitive to folate pathway inhibitors (sulfachloropyridazine, p-aminosalicylic acid, sulfamethoxazole, and trimethoprim). The studies reveal that MTHFR1 and MTHFR2 are two noncanonical MTHFR proteins that are monomeric and lack flavin coenzyme. Both MTHFR1 and MTHFR2 are involved in de novo methionine biosynthesis and required for antifolate resistance in mycobacteria.IMPORTANCE MTHFR/MetF is an essential enzyme in a one-carbon metabolic pathway for de novo biosynthesis of methionine. MTHFRs are known to be oligomeric flavoproteins. Our in vivo and in vitro analyses of Mycobacterium smegmatis MSMEG_6664/MSMEI_6484, annotated as putative MTHFR, failed to reveal their function as MTHFRs. However, we identified two of the hypothetical proteins, MSMEG_6596 and MSMEG_6649, as MTHFR1 and MTHFR2, respectively. Interestingly, both MTHFRs are monomeric and lack flavin coenzymes. M. smegmatis deleted for the major mthfr (mthfr1) was partially auxotroph for methionine and more sensitive to folate pathway inhibitors (sulfachloropyridazine, para-aminosalicylic acid, sulfamethoxazole, and trimethoprim). The studies reveal that MTHFR1 and MTHFR2 are novel MTHFRs involved in de novo methionine biosynthesis and required for antifolate resistance in mycobacteria.