Investigating inhibitors of 1-deoxy-d-xylulose 5-phosphate synthase in a mouse model of UTI.

The rising rate of antimicrobial resistance continues to threaten global public health. Further hastening antimicrobial resistance is the lack of new antibiotics against new targets. The bacterial enzyme, 1-deoxy-d-xylulose 5-phosphate synthase (DXPS), is thought to play important roles in central metabolism, including processes required for pathogen adaptation to fluctuating host environments. Thus, impairing DXPS function represents a possible new antibacterial strategy. We previously investigated a DXPS-dependent metabolic adaptation as a potential target in uropathogenic Escherichia coli (UPEC) associated with urinary tract infection (UTI), using the DXPS-selective inhibitor butyl acetylphosphonate (BAP). However, investigations of DXPS inhibitors in vivo have not been conducted. The goal of the present study is to advance DXPS inhibitors as in vivo probes and assess the potential of inhibiting DXPS as a strategy to prevent UTI in vivo. We show that BAP was well-tolerated at high doses in mice and displayed a favorable pharmacokinetic profile for studies in a mouse model of UTI. Further, an alkyl acetylphosphonate prodrug (homopropargyl acetylphosphonate, pro-hpAP) was significantly more potent against UPEC in urine culture and exhibited good exposure in the urinary tract after systemic dosing. Prophylactic treatment with either BAP or pro-hpAP led to a partial protective effect against UTI, with the prodrug displaying improved efficacy compared to BAP. Overall, our results highlight the potential for DXPS inhibitors as in vivo probes and establish preliminary evidence that inhibiting DXPS impairs UPEC colonization in a mouse model of UTI.IMPORTANCENew antibiotics against new targets are needed to prevent an antimicrobial resistance crisis. Unfortunately, antibiotic discovery has slowed, and many newly FDA-approved antibiotics do not inhibit new targets. Alkyl acetylphosphonates (alkyl APs), which inhibit the enzyme 1-deoxy-d-xylulose 5-phosphate synthase (DXPS), represent a new possible class of compounds as there are no FDA-approved DXPS inhibitors. To our knowledge, this is the first study demonstrating the in vivo safety, pharmacokinetics, and efficacy of alkyl APs in a urinary tract infection mouse model.

High Target Homology Does Not Guarantee Inhibition: Aminothiazoles Emerge as Inhibitors of Plasmodium falciparum.

In this study, we identified three novel compound classes with potent activity against Plasmodium falciparum, the most dangerous human malarial parasite. Resistance of this pathogen to known drugs is increasing, and compounds with different modes of action are urgently needed. One promising drug target is the enzyme 1-deoxy-d-xylulose-5-phosphate synthase (DXPS) of the methylerythritol 4-phosphate (MEP) pathway for which we have previously identified three active compound classes against Mycobacterium tuberculosis. The close structural similarities of the active sites of the DXPS enzymes of P. falciparum and M. tuberculosis prompted investigation of their antiparasitic action, all classes display good cell-based activity. Through structure-activity relationship studies, we increased their antimalarial potency and two classes also show good metabolic stability and low toxicity against human liver cells. The most active compound 1 inhibits the growth of blood-stage P. falciparum with an IC50 of 600 nM. The results from three different methods for target validation of compound 1 suggest no engagement of DXPS. All inhibitor classes are active against chloroquine-resistant strains, confirming a new mode of action that has to be further investigated.

1-deoxy-D-xylulose-5-phosphate synthase from Pseudomonas aeruginosa and Klebsiella pneumoniae reveals conformational changes upon cofactor binding.

The ESKAPE bacteria are the six highly virulent and antibiotic-resistant pathogens that require the most urgent attention for the development of novel antibiotics. Detailed knowledge of target proteins specific to bacteria is essential to develop novel treatment options. The methylerythritol-phosphate (MEP) pathway, which is absent in humans, represents a potentially valuable target for the development of novel antibiotics. Within the MEP pathway, the enzyme 1-deoxy-D-xylulose-5-phosphate synthase (DXPS) catalyzes a crucial, rate-limiting first step and a branch point in the biosynthesis of the vitamins B1 and B6. We report the high-resolution crystal structures of DXPS from the important ESKAPE pathogens Pseudomonas aeruginosa and Klebsiella pneumoniae in both the co-factor-bound and the apo forms. We demonstrate that the absence of the cofactor thiamine diphosphate results in conformational changes that lead to disordered loops close to the active site that might be important for the design of potent DXPS inhibitors. Collectively, our results provide important structural details that aid in the assessment of DXPS as a potential target in the ongoing efforts to combat antibiotic resistance.

DXP Synthase Function in a Bacterial Metabolic Adaptation and Implications for Antibacterial Strategies.

Pathogenic bacteria possess a remarkable ability to adapt to fluctuating host environments and cause infection. Disturbing bacterial central metabolism through inhibition of 1-deoxy-d-xylulose 5-phosphate synthase (DXPS) has the potential to hinder bacterial adaptation, representing a new antibacterial strategy. DXPS functions at a critical metabolic branchpoint to produce the metabolite DXP, a precursor to pyridoxal-5-phosphate (PLP), thiamin diphosphate (ThDP) and isoprenoids presumed essential for metabolic adaptation in nutrient-limited host environments. However, specific roles of DXPS in bacterial adaptations that rely on vitamins or isoprenoids have not been studied. Here we investigate DXPS function in an adaptation of uropathogenic E. coli (UPEC) to d-serine (d-Ser), a bacteriostatic host metabolite that is present at high concentrations in the urinary tract. UPEC adapt to d-Ser by producing a PLP-dependent deaminase, DsdA, that converts d-Ser to pyruvate, pointing to a role for DXPS-dependent PLP synthesis in this adaptation. Using a DXPS-selective probe, butyl acetylphosphonate (BAP), and leveraging the toxic effects of d-Ser, we reveal a link between DXPS activity and d-Ser catabolism. We find that UPEC are sensitized to d-Ser and produce sustained higher levels of DsdA to catabolize d-Ser in the presence of BAP. In addition, BAP activity in the presence of d-Ser is suppressed by ß-alanine, the product of aspartate decarboxylase PanD targeted by d-Ser. This BAP-dependent sensitivity to d-Ser marks a metabolic vulnerability that can be exploited to design combination therapies. As a starting point, we show that combining inhibitors of DXPS and CoA biosynthesis displays synergy against UPEC grown in urine where there is increased dependence on the TCA cycle and gluconeogenesis from amino acids. Thus, this study provides the first evidence for a DXPS-dependent metabolic adaptation in a bacterial pathogen and demonstrates how this might be leveraged for development of antibacterial strategies against clinically relevant pathogens.

Metabolomes and transcriptomes revealed the saponin distribution in root tissues of Panax quinquefolius and Panax notoginseng.

BACKGROUND: Panax quinquefolius and Panax notoginseng are widely used and well known for their pharmacological effects. As main pharmacological components, saponins have different distribution patterns in the root tissues of Panax plants. METHODS: In this study, the representative ginsenosides were detected and quantified by desorption electrospray ionization mass spectrometry and high-performance liquid chromatography analysis to demonstrate saponin distribution in the root tissues of P. quinquefolius and P. notoginseng, and saponin metabolite profiles were analyzed by metabolomes to obtain the biomarkers of different root tissues. Finally, the transcriptome analysis was performed to demonstrate the molecular mechanisms of saponin distribution by gene profiles. RESULTS: There was saponin distribution in the root tissues differed between P. quinquefolius and P. notoginseng. Eight-eight and 24 potential biomarkers were detected by metabolome analysis, and a total of 340 and 122 transcripts involved in saponin synthesis that were positively correlated with the saponin contents (R > 0.6, P < 0.05) in the root tissues of P. quinquefolius and P. notoginseng, respectively. Among them, GDPS1, CYP51, CYP64, and UGT11 were significantly correlated with the contents of Rg1, Re, Rc, Rb2, and Rd in P. quinquefolius. UGT255 was markedly related to the content of R1; CYP74, CYP89, CYP100, CYP103, CYP109, and UGT190 were markedly correlated with the Rd content in P. notoginseng. CONCLUSIONS: These results provided the visual and quantitative profiles of and confirmed the pivotal transcripts of CYPs and UGTs regulating the saponin distribution in the root tissues of P. quinquefolius and P. notoginseng.

X-ray crystallography-based structural elucidation of enzyme-bound intermediates along the 1-deoxy-d-xylulose 5-phosphate synthase reaction coordinate.

1-Deoxy-d-xylulose 5-phosphate synthase (DXPS) uses thiamine diphosphate (ThDP) to convert pyruvate and d-glyceraldehyde 3-phosphate (d-GAP) into 1-deoxy-d-xylulose 5-phosphate (DXP), an essential bacterial metabolite. DXP is not utilized by humans; hence, DXPS has been an attractive antibacterial target. Here, we investigate DXPS from Deinococcus radiodurans (DrDXPS), showing that it has similar kinetic parameters Kmd-GAP and Kmpyruvate (54 ± 3 and 11 ± 1 µm, respectively) and comparable catalytic activity (kcat = 45 ± 2 min-1) with previously studied bacterial DXPS enzymes and employing it to obtain missing structural data on this enzyme family. In particular, we have determined crystallographic snapshots of DrDXPS in two states along the reaction coordinate: a structure of DrDXPS bound to C2α-phosphonolactylThDP (PLThDP), mimicking the native pre-decarboxylation intermediate C2α-lactylThDP (LThDP), and a native post-decarboxylation state with a bound enamine intermediate. The 1.94-Å-resolution structure of PLThDP-bound DrDXPS delineates how two active-site histidine residues stabilize the LThDP intermediate. Meanwhile, the 2.40-Å-resolution structure of an enamine intermediate-bound DrDXPS reveals how a previously unknown 17-Å conformational change removes one of the two histidine residues from the active site, likely triggering LThDP decarboxylation to form the enamine intermediate. These results provide insight into how the bi-substrate enzyme DXPS limits side reactions by arresting the reaction on the less reactive LThDP intermediate when its cosubstrate is absent. They also offer a molecular basis for previous low-resolution experimental observations that correlate decarboxylation of LThDP with protein conformational changes.

Integrated metabolomic and transcriptomic analyses revealed the distribution of saponins in Panax notoginseng.

Panax notoginseng is famous for its important therapeutic effects. Saponins are bioactive compounds found in different parts and developmental stages of P. notoginseng plants. Thus, it is urgently to study saponins distribution in different parts and growth ages of P. notoginseng plants. In this study, potential biomarkers were found, and their chemical characteristic differences were revealed through metabolomic analysis. High-performance liquid chromatography data indicated the higher content of saponins (i.e., Rg1, Re, Rd, and Rb1) in the underground parts than that in the aerial parts. 20(S)-Protopanaxadiol saponins were mainly distributed in the aerial parts. Additionally, the total saponin content in the 3-year-old P. notoginseng plant (188.0 mg/g) was 1.4-fold higher than that in 2-year-old plant (130.5 mg/g). The transcriptomic analysis indicated the tissue-specific transcription expression of genes, namely, PnFPS, PnSS, PnSE1, PnSE2, and PnDS, which encoded critical synthases in saponin biosyntheses. These genes showed similar expression patterns among the parts of P. notoginseng plants. The expression levels of these genes in the flowers and leaves were 5.2fold higher than that in the roots and fibrils. These results suggested that saponins might be actively synthesized in the aerial parts and transformed to the underground parts. This study provides insights into the chemical and genetic characteristics of P. notoginseng to facilitate the synthesis of its secondary metabolites and a scientific basis for appropriate collection and rational use of this plant.