Synergistic efficacy of Bisbenzimidazole and Carbonyl Cyanide 3-Chlorophenylhydrazone combination against MDR bacterial strains

Elucidation of the Microwave-Assisted Synthesis and Characterization of Heteronuclear Complexes of Bisbenzimidazole Derivatives and Their Biological Activities by In Vitro and In Silico Assays

A novel and efficient protocol for the microwave-assisted synthesis of diversely substituted 2,2'-bisbenzimidazol-5,6'-dicarboxylic acid (BIMCA) from the reaction of 3,4-diaminobenzoic acid with oxalic acid has been developed, which proceeds through sequential nucleophilic addition and electrophilic substitution in accordance with the Philips method. The synthetic utility of this strategy was demonstrated by the concise, one-pot synthesis of (BIMCA) and metal complexes. (BIMCA) with a [{Fe(salen)}2O] Schiff base ligand complex and new benzimidazole coordination compounds with double oxygen [(BIMCA){Fe(salen)}2] ligand complexes were obtained. The resulting [(BIMCA){Fe(salen)}2] ligand complex was then synthesized from Co(CH3COO)2.4H2O, Ni(CH3COO)2.4H2O and Cu(CH3COO)2.H2O heteronuclear complexes. The condensations proceed with good yield to give products that, in certain instances, are not readily attainable by conventional condensation techniques. The structures of the compounds were identified by Fourier-transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (1H NMR), elemental analysis and magnetic susceptibility. The mutagenic potential of the synthesized chemicals was evaluated by the Ames test towards mutant Salmonella typhimurium strains TA98 and TA100. It was recorded that these chemicals had no mutagenic action. Also, antimicrobial activities were screened by broth microdilution test. It was seen that the minimum inhibitory concentration (MIC) against Klebsiella pneumoniae, Staphylococcus aureus and Staphylococcus epidermidis was 0.195 mg/mL, followed by a MIC value of 0.390 mg/mL against Escherichia coli and Salmonella typhimurium. [(BIMCA){Fe(salen)}2Co(II)] demonstrated significant antimicrobial activity against Proteus mirabilis and Staphylococcus aureus, with an MIC of 0.195 mg/mL, followed by an MIC of 0.390 mg/mL against Pseudomonas aeruginosa, K. pneumonia and Salmonella typhimurium. The antioxidant properties were examined using various chemical assays, and [(BIMCA){Fe(salen)}2O] and (BIMCA) exhibited greater 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging ability, when compared with other compounds. Enzyme inhibitory effects were tested against acetylcholinesterase (AChE), amylase, butyrylcholinesterase (BChE) and tyrosinase. [(BIMCA){Fe(salen)}2Cu(II)] displayed the best AChE (IC50 0.51 mg/mL), BChE (IC50 0.51 mg/mL) and tyrosinase (IC50 1.52 mg/mL) inhibitory effects. Furthermore, molecular docking calculations were performed to gain insights into the interaction between [(BIMCA){Fe(salen)}2] and AChE, and between [(BIMCA){Fe(salen)}2Cu(II)] and amylase. Both compounds showed the potential inhibition of the protein targets.

Influence of carbonyl cyanide m-chlorophenyl hydrazone on biofilm dynamics, protease, and siderophore production by Burkholderia pseudomallei

Efflux pump inhibitors are a potential therapeutic strategy for managing antimicrobial resistance and biofilm formation. This article evaluated the effect of carbonyl cyanide m-chlorophenyl hydrazone (CCCP) on the biofilm growth dynamics and the production of virulence factors by Burkholderia pseudomallei. The effects of CCCP on planktonic, growing, and mature biofilm, interaction with antibacterial drugs, and protease and siderophore production were assessed. CCCP MICs ranged between 128 and 256 µM. The CCCP (128 µM) had a synergic effect with all the antibiotics tested against biofilms. Additionally, CCCP reduced (p < .05) the biomass of biofilm growth and mature biofilms at 128 and 512 µM, respectively. CCCP also decreased (p < .05) protease production by growing (128 µM) and induced (p < .05) siderophore release by planktonic cells (128 µM) growing biofilms (12.8 and 128 µM) and mature biofilms (512 µM). CCCP demonstrates potential as a therapeutic adjuvant for disassembling B. pseudomallei biofilms and enhancing drug penetration.

Polydispersity-mediated high efficacy of an in-situ aqueous nanosuspension of PPEF.3HCl in methicillin resistant Staphylococcus aureus sepsis model

Recently, World Health Organization declared antimicrobial resistance as the third greatest threat to human health. Absence of known cross-resistance, new class, new target, and a new mode of action are few major strategies being undertaken by researches to combat multidrug resistant pathogen. PPEF.3HCl, a bisbenzimidazole was developed as highly potent antibacterial agent against ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) pathogens, targeting topoisomerase IA. The present work encompasses a radical on-site generation of In-situ nanosuspension of PPEF.3HCl with enhanced efficacy against methicillin resistant S. aureus in septicemia model. We have generated instantaneously a PPEF.3HCl nanosuspension (IsPPEF.3HCl-NS) by mixing optimized monophasic PPEF.3HCl preconcentrate in propylene glycol into an aqueous medium comprising tween 80 as stabilizer. The IsPPEF.3HCl-NS showed precipitation efficiency of > 90 %, average particle size < 500 nm, retained upto 5 h, a negative zeta potential and bi/trimodal particle size distribution. Differential scanning calorimetry, X-ray diffraction confirmed partial amorphization and transmission electron microscopy revealed spherical particles. IsPPEF.3HCl-NS was non-hemolytic and exhibited good stability in serum. More significantly, it exhibited a ∼ 1.6-fold increase in macrophage uptake compared to free PPEF.3HCl in the RAW 264.7 macrophage cell line. Confocal microscopy revealed accumulation of IsPPEF.3HCl-NS within the lysosomal compartment and cell cytosol, proposing high efficacy. In terms of antimicrobial efficacy, IsPPEF.3HCl-NS outperforms free PPEF.3HCl against clinical methicillin sensitive and resistant S. aureus strains. In a pivotal experiment, IsPPEF.3HCl-NS exhibited over 83 % survival at 8 mg/kg.bw and an impressive reduction of ∼ 4-5 log-fold in bacterial load, primarily in the kidney, liver and spleen of septicemia mice. IsPPEF.3HCl-NS prepared by the In-situ approach, coupled with enhanced intramacrophage delivery and superior efficacy, positions IsPPEF.3HCl-NS as a pioneering and highly promising formulation in the battle against antimicrobial resistance.

Unraveling topoisomerase IA gate dynamics in presence of PPEF and its preclinical evaluation against multidrug-resistant pathogens

Type IA topoisomerases maintain DNA topology by cleaving ssDNA and relaxing negative supercoils. The inhibition of its activity in bacteria prevents the relaxation of negative supercoils, which in turn impedes DNA metabolic processes leading to cell death. Using this hypothesis, two bisbenzimidazoles, PPEF and BPVF are synthesized, selectively inhibiting bacterial TopoIA and TopoIII. PPEF stabilizes the topoisomerase and topoisomerase-ssDNA complex, acts as an interfacial inhibitor. PPEF display high efficacy against ~455 multi-drug resistant gram positive and negative bacteria. To understand molecular mechanism of inhibition of TopoIA and PPEF, accelerated MD simulation is carried out, and results suggested that PPEF binds, stabilizes the closed conformation of TopoIA with -6Kcal/mol binding energy and destabilizes the binding of ssDNA. The TopoIA gate dynamics model can be used as a tool to screen TopoIA inhibitors as therapeutic candidates. PPEF and BPVF cause cellular filamentation and DNA fragmentation leading to bacterial cell death. PPEF and BPVF show potent efficacy against systemic and neutropenic mouse models harboring E. coli, VRSA, and MRSA infection without cellular toxicity.

Moonlighting proteins: beacon of hope in era of drug resistance in bacteria

Moonlighting proteins (MLPs) are ubiquitous and provide a unique advantage to bacteria performing multiple functions using the same genomic content. Targeting MLPs can be considered as a futuristic approach in fighting drug resistance problem. This review follows the MLP trail from its inception to the present-day state, describing a few bacterial MLPs, viz., glyceraldehyde 3'-phosphate dehydrogenase, phosphoglucose isomerase glutamate racemase (GR), and DNA gyrase. Here, we carve out that targeting MLPs are the beacon of hope in an era of increasing drug resistance in bacteria. Evolutionary stability, structure-functional relationships, protein diversity, possible drug targets, and identification of new drugs against bacterial MLP are given due consideration. Before the final curtain calls, we provide a comprehensive list of small molecules that inhibit the biochemical activity of MLPs, which can aid the development of novel molecules to target MLPs for therapeutic applications.

Pixantrone confers radiosensitization in KRAS mutated cancer cells by suppression of radiation-induced prosurvival pathways

Radioresistance towards radiation therapy has generated the need for the development of radiosensitizers as a potential drug. KRAS mutation brings radioresistance in tumor cells. The present work proves sensitization of cancer cells towards radiotherapy through inhibition of KRAS activation. Acquiring a drug repurposing approach, the in-silico screening revealed that pixantrone, an antineoplastic drug, possesses a high affinity towards KRAS G12C and G12D subtypes. The SPR study suggests that maximum affinity of pixantrone was observed with KRAS G12C>WT>G12D and G12S. Pixantrone potentially inhibited the KRAS activation in stable transfectants G12C and G12D cell lines and radiosensitized distinct KRAS mutant subtype cells. The combination of pixantrone with radiation causes enhanced dsDNA breaks along with enhanced ATM expression, and increased late apoptosis. The preclinical studies on NCr-fox1^nu xenograft mice showed potent inhibition of tumor progression and prolonged survival of mcie due to the radiosensitizing effect of pixantrone. Radiation-induced activation of key effector proteins of RAS downstream pathways, like MAPK and PI3K/Akt/mTOR pathways, were downregulated in tumor cells upon combination treatment. Interestingly, a robust upregulation of senescence marker p21 was observed in the tumor cells in combination treatment. These findings reveal a convergence between KRAS signaling, pixantrone treatment, and radiation conferring tumor cell death.

An antibacterial compound pyrimidomycin produced by Streptomyces sp. PSAA01 isolated from soil of Eastern Himalayan foothill

Selective isolation of soil Actinobacteria was undertaken to isolate a new class of antibiotics and bioactive molecules. A Streptomyces sp. PSAA01 (= MTCC 13,157), isolated from soil of Eastern Himalaya foothill was cultivated on a large scale for the production of the antimicrobial SM02. It has been found that the maximum amount of SM02 produced while PSAA01 was grown in ISP-2 medium (pH 7.0) for 7 days at 30 °C in shaking (180 rpm) condition. A significant zone of inhibition against Staphylococcus aureus MTCC 96 has been found with the crude cell-free culture media (50 µL) of 7 days grown PSAA01. After the purification and chemical structural characterization, we found that SM02 is a new antimicrobial having 746 dalton molecular weight. The compound SM02 contains pyrimidine moiety in it and is produced by a species of Streptomyces and thus we have named this antibiotic pyrimidomycin. The antimicrobial spectrum of pyrimidomycin has been found to be restricted in Gram-positive organisms with a MIC of 12 µg/mL. SM02 was found active against Mycobacterium sp. and also multi-drug resistant Gram-positive bacteria with similar potency and found to disrupt the bacterial cell wall. Pyrimidomycin also showed significant impairment in the biofilm formation by S. aureus. Furthermore, pyrimidomycin showed synergy with the most used antibiotic like ampicillin, vancomycin and chloramphenicol. Pyrimidomycin did not have cytotoxicity towards human cell lines indicating its limited activity within bacteria.

The antimicrobial and immunomodulatory effects of Ionophores for the treatment of human infection

Ionophores are a diverse class of synthetic and naturally occurring ion transporter compounds which demonstrate both direct and in-direct antimicrobial properties against a broad panel of bacterial, fungal, viral and parasitic pathogens. In addition, ionophores can regulate the host-immune response during communicable and non-communicable disease states. Although the clinical use of ionophores such as Amphotericin B, Bedaquiline and Ivermectin highlight the utility of ionophores in modern medicine, for many other ionophore compounds issues surrounding toxicity, bioavailability or lack of in vivo efficacy studies have hindered clinical development. The antimicrobial and immunomodulating properties of a range of compounds with characteristics of ionophores remain largely unexplored. As such, ionophores remain a latent therapeutic avenue to address both the global burden of antimicrobial resistance, and the unmet clinical need for new antimicrobial therapies. This review will provide an overview of the broad-spectrum antimicrobial and immunomodulatory properties of ionophores, and their potential uses in clinical medicine for combatting infection.

Effect of metabolic uncouplers on the performance of toluene-degrading biotrickling filter

The biomass control potential of three metabolic uncouplers (carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP), carbonyl cyanide m-chlorophenylhydrazone (CCCP), and m-chlorophenol (m-CP)) was tested in biotrickling filters (BTFs) degrading toluene. The experiments employed two types of reactors: a traditional column design and a novel differential BTF (DBTF) reactor developed by De Vela and Gostomski (J Environ Eng 147:04020159, 2021). Uncouplers caused the toluene elimination capacity (EC) (~33 g/m3h for column reactors and ~600 g/m3h for DBTF) to decrease by 15-97% in a dose-dependent fashion. The EC completely recovered in the column reactor in 3 to 13 days, while only partial recovery happened in the DBTF. Short-term (1 to 3 days) true uncoupling was indicated by the 20-160% increase in %CO2 recovery, depending on concentration. FCCP and CCCP increased the pressure drop due to increased extracellular polymeric substances (EPS) production for protection against the uncouplers. The 4.0-mM m-CP weakened the biofilm in the BTF bed, as evidenced by the 130-500% increase in the total organic carbon in the liquid sump of the column and DBTF reactors. Moreover, a microbial shift led to the proliferation of genera that degrade uncouplers, further demonstrating that the uncouplers tested were not a sustainable biomass control strategy in BTFs.

Combination therapy of biogenic C-dots and lysozyme for enhanced antibacterial and antibiofilm activity

Nearly 80% of human chronic infections are caused due to bacterial biofilm formation. The increased resistance against the conventional antimicrobial agents makes it difficult to treat the biofilm-related infections. The antibiotics resistance developed by planktonic cells has also become a major threat for human. Therefore, we have attempted here to develop an effective alternative strategy to overcome the issues of antibiotics resistance of bacteria. Upon synthesis, biogenic C-dots were combined with lysozymes which were further encapsulated into chitosan nanocarrier to form C-dots carrier (CDC). The as-synthesized C-dots were found irregular shaped and the average size of C-dots and CDC were 8 ± 2 nm and 450 ± 50 nm, respectively. To ensure secure and targeted delivery of C-dots and lysozyme we have employed chitosan, a biodegradable and natural biopolymer, as a delivery system. The study of time-dependent bacterial growth and flow cytometry analysis demonstrated that CDC can exhibit a synergistic bactericidal activity against the antibiotics resistant recombinant E. coli cells. Further, we have shown that the CDC could be a potent agent for both prevention of biofilm formation and eradication of preformed biofilm. In addition, we have observed that our drug delivery system is hemocompatible in nature making it suitable for in vivo applications. Therefore, we believe that the combination therapy of C-dots and lysozyme may be used as an excellent antibacterial and antibiofilm strategy.

Recent Advances in Therapeutic Applications of Bisbenzimidazoles

Nitrogen-containing heterocycles are one of the most common structural motifs in approximately 80% of the marketed drugs. Of these, benzimidazoles analogues are known to elicit a wide spectrum of pharmaceutical activities such as anticancer, antibacterial, antiparasitic, antiviral, antifungal as well as chemosensor effect. Based on the benzimidazole core fused heterocyclic compounds, crescent-shaped bisbenzimidazoles were developed which provided an early breakthrough in the sequence-specific DNA recognition. Over the years, a number of functional variations in the bisbenzimidazole core have led to the emergence of their unique properties and established them as versatile ligands against several classes of pathogens. The present review provides an overview of diverse pharmacological activities of the bisbenzimidazole analogues in the past decade with a brief account of its development through the years.

Potential anti-TB investigational compounds and drugs with repurposing potential in TB therapy: a conspectus

The latest WHO report estimates about 1.6 million global deaths annually from TB, which is further exacerbated by drug-resistant (DR) TB and comorbidities with diabetes and HIV. Exiguous dosing, incomplete treatment course, and the ability of the tuberculosis bacilli to tolerate and survive current first-line and second-line anti-TB drugs, in either their latent state or active state, has resulted in an increased prevalence of multidrug-resistant (MDR), extensively drug-resistant (XDR), and totally drug-resistant TB (TDR-TB). Although a better understanding of the TB microanatomy, genome, transcriptome, proteome, and metabolome, has resulted in the discovery of a few novel promising anti-TB drug targets and diagnostic biomarkers of late, no new anti-TB drug candidates have been approved for routine therapy in over 50 years, with only bedaquiline, delamanid, and pretomanid recently receiving tentative regulatory approval. Considering this, alternative approaches for identifying possible new anti-TB drug candidates, for effectively eradicating both replicating and non-replicating Mycobacterium tuberculosis, are still urgently required. Subsequently, several antibiotic and non-antibiotic drugs with known treatment indications (TB targeted and non-TB targeted) are now being repurposed and/or derivatized as novel antibiotics for possible use in TB therapy. Insights gathered here reveal that more studies focused on drug-drug interactions between licensed and potential lead anti-TB drug candidates need to be prioritized. This write-up encapsulates the most recent findings regarding investigational compounds with promising anti-TB potential and drugs with repurposing potential in TB therapy.

Effect of new carbonyl cyanide aromatic hydrazones on biofilm inhibition against methicillin resistant Staphylococcus aureus

Carbonyl cyanide m-chlorophenylhydrazone (CCCP), as a protonophore, in combination with antibiotics exhibited potentiating antibacterial activity. To improve CCCP's potency and toxicity, a series of aromatic hydrazones were synthesized and their antimicrobial activity was evaluated; amongst them, compounds 2e and 2j with a strong para-electron-withdrawing substituent (–NO₂ and –CF₃) at the phenyl ring had the lowest MICs against both S. aureus and methicillin resistant Staphylococcus aureus (1.56 and 1.56 μM, respectively). Some compounds in combination with antibiotics exhibited potentiate Gram-positive antibacterial activity; compound 2e was found to display unaided or synergistic efficacy against MRSA. In particular, when compound 2e is combined with ofloxacin, it has a good synergistic effect against MRSA. Moreover, electron microscopy revealed that compound 2e inhibits biofilm formation and effectively eradicates preformed biofilm. MTT assay showed that compound 2e displays as low toxicity as CCCP. Overall, our data showed that the aromatic hydrazone is a promising scaffold for anti-staphylococcal drug development.

2e and 2j with strong p-NO₂ and p-CF₃ at phenyl ring had the lowest MICs against S. aureus and MRSA. 2e displayed unaided or synergistic efficacy against MRSA, especially combined with ofloxacin. EM revealed that 2e destroys biofilms and cell membranes.

Synergistic Actions of Benzyl Isothiocyanate with Ethylenediaminetetraacetic Acid and Efflux Pump Inhibitor Phenylalanine-Arginine β-Naphthylamide Against Multidrug-Resistant Escherichia coli

The aim of this study was to assess the efficacy of benzyl isothiocyanate (BITC) in combination with efflux inhibitors and metal chelators against multidrug-resistant Escherichia coli. In vitro synergism between testing molecules was observed based on the minimal inhibitory concentration (MIC), minimal bactericidal concentration (MBC), fractional inhibitory concentration index (FICI), bactericidal kinetics, and growth inhibition assay. BITC alone exhibited moderate antibacterial activity against E. coli strains with MIC and MBC values of 0.625-1.25 μM and 1.25-2.5 μM, respectively. In contrast, double and triple combinations of BITC, ethylenediaminetetraacetic acid (EDTA), and phenylalanine-arginine β-naphthylamide (PAβN) resulted in synergistic activities with FICI values between 0.18 and 0.5, whereas combination of BITC with carbonyl cyanide m-chlorophenyl hydrazone or 2, 2'-dipyridyl revealed additive or indifference effect with FICI values of 0.75-1.5 and 1-1.5, respectively. Results of bactericidal kinetics and growth inhibition assays also supported the synergistic effects of EDTA and PAβN with BITC against E. coli strains. Our data demonstrate the possible use of adjuvant agents, such as the chelating agent EDTA and the efflux inhibitor PAβN to improve the antibacterial potential of isothiocyanate and may help to develop an alternative strategy for reducing the occurrence of multidrug resistance.

Gram-negative synergy and mechanism of action of alkynyl bisbenzimidazoles

Bisbenzimidazoles with terminal alkynyl linkers, selective inhibitors of bacterial topoisomerase I, have been evaluated using bacterial cytological profiling (BCP) to ascertain their mechanism of action and screened for synergism to improve Gram-negative bacterial coverage. Principal component analysis of high throughput fluorescence images suggests a dual-mechanism of action affecting DNA synthesis and cell membrane integrity. Fluorescence microscopy of bacteria challenged with two of the alkynyl-benzimidazoles revealed changes in the cellular ultrastructure that differed from topoisomerase II inhibitors including induction of spheroplasts and membrane lysis. The cytoskeleton recruitment enzyme inhibitor A22 in combination with one of the alkynyl-benzimidazoles was synergistic against Acinetobacter baumannii and Escherichia coli. Gram-positive coverage remained unchanged in the A22-alkynyl bisbenzimidazole combination. Efflux inhibitors were not synergistic, suggesting that the Gram-negative outer membrane was a significant barrier for alkynyl-bisbenzimidazole uptake. Time-kill assays demonstrated the A22-bisbenzimidazole combination had a similar growth inhibition curve to that of norfloxacin in E.coli. Bisbenzimidazoles with terminal alkynyl linkers likely impede bacterial growth by compromising cell membrane integrity and by interfering with DNA synthesis against Gram-positive pathogens and in the synergistic combination against Gram-negative pathogens including E. coli and multidrug-resistant A. baumanii.

Efflux pump inhibitor CCCP to rescue colistin susceptibility in mcr-1 plasmid-mediated colistin-resistant strains and Gram-negative bacteria

Objectives

Efflux in bacteria is a ubiquitous mechanism associated with resistance to antimicrobials agents. Efflux pump inhibitors (EPIs) have been developed to inhibit efflux mechanisms and could be a good alternative to reverse colistin resistance, but only CCCP has shown good activity. The aim of our study was to identify CCCP activity in a collection of 93 Gram-negative bacteria with known and unknown colistin resistance mechanisms including isolates with mcr-1 plasmid-mediated colistin resistance.

Methods

Colistin MIC was evaluated with and without CCCP and the fold decrease of colistin MIC was calculated for each strain. In order to evaluate the effect of this combination, a time-kill study was performed on five strains carrying different colistin resistance mechanisms.

Results

Overall, CCCP was able to reverse colistin resistance for all strains tested. The effect of CCCP was significantly greater on intrinsically colistin-resistant bacteria (i.e. Proteus spp., Serratia marcescens, Morganella morganii and Providencia spp.) than on other Enterobacteriaceae (P < 0.0001). The same was true for bacteria with a heteroresistance mechanism compared to bacteria with other colistin resistance mechanisms (P < 0.0001). A time-kill study showed the combination was bacteriostatic on strains tested.

Conclusions

These results suggest an efflux mechanism, especially on intrinsically resistant bacteria and Enterobacter spp., but further analysis is needed to identify the molecular support of this mechanism. EPIs could be an alternative for restoring colistin activity in Gram-negative bacteria. Further work is necessary to identify new EPIs that could be used in humans.

PPEF: A bisbenzimdazole potent antimicrobial agent interacts at acidic triad of catalytic domain of E. coli topoisomerase IA

BACKGROUND

Topoisomerase is a well known target to develop effective antibacterial agents. In pursuance of searching novel antibacterial agents, we have established a novel bisbenzimidazole (PPEF) as potent E. coli topoisomerase IA poison inhibitor.

METHODS

In order to gain insights into the mechanism of action of PPEF and understanding protein-ligand interactions, we have produced wild type EcTopo 67 N-terminal domain (catalytic domain) and its six mutant proteins at acidic triad (D111, D113, E115). The DDE motif is replaced by alanine (A) to create three single mutants: D111A, D113A, E115A and three double mutants: D111A-D113A, D113A-E115A and D111A-E115A.

RESULTS

Calorimetric study of PPEF with single mutants showed 10 fold lower affinity than that of wild type EcTopo 67 (7.32 × 10⁶ M^-1for wild type, 0.89 × 10⁶ M^-1for D111A) and 100 fold lower binding with double mutant D113A-E115A (0.02 × 10⁶ M^-1) was observed. The mutated proteins showed different CD signature as compared to wild type protein. CD and fluorescence titrations were done to study the interaction between EcTopo 67 and ligands. Molecular docking study validated that PPEF has decreased binding affinity towards mutated enzymes as compared to wild type.

CONCLUSION

The overall study reveals that PPEF binds to D113 and E115 of acidic triad of EcTopo 67. Point mutations decrease binding affinity of PPEF towards DDE motif of topoisomerase.

GENERAL SIGNIFICANCE

This study concludes PPEF as poison inhibitor of E. coli Topoisomerase IA, which binds to acidic triad of topoisomerase IA, responsible for its function. PPEF can be considered as therapeutic agent against bacteria.