Mechanism Of Inhibition Research Articles

Design, Synthesis, and Anti-Melanogenic Activity of 2-Mercaptomethylbenzo[d]imidazole Derivatives Serving as Tyrosinase Inhibitors: An In Silico, In Vitro, and In Vivo Exploration.

2-Mercaptomethylbenzo[d]imidazole (2-MMBI) derivatives were designed and synthesized as tyrosinase (TYR) chelators using 2-mercaptomethylimidazole scaffolds. Seven of the ten 2-MMBI derivatives exhibited stronger inhibition of mushroom TYR activity than kojic acid. Their ability to chelate copper ions was demonstrated through experiments using the copper chelator pyrocatechol violet and assays measuring TYR activity in the presence or absence of exogenous CuSO4. The inhibition mechanisms of derivatives 1, 3, 8, and 9, which showed excellent TYR inhibitory activity, were elucidated through kinetic studies and supported by the docking simulation results. Derivatives 3, 7, 8, and 10 significantly inhibited cellular TYR activity and melanin production in B16F10 cells in a dose-dependent manner, with stronger potency than kojic acid. Furthermore, in situ, derivatives 7 and 10 showed stronger inhibitory effects on B16F10 cell TYR activity than kojic acid. Six derivatives, including 8, showed highly potent depigmentation in zebrafish larvae, outpacing kojic acid even at 200-670 times lower concentrations. Additionally, all derivatives could scavenge for reactive oxygen species without causing cytotoxicity in epidermal cells. These results suggested that 2-MMBI derivatives are promising anti-melanogenic agents.

Chemoinformatics for corrosion science: Data-driven modeling of corrosion inhibition by organic molecules.

This paper reviews the application of machine learning to the inhibition of corrosion by organic molecules. The methodologies considered include quantitative structure-property relationships (QSPR) and related data-driven approaches. The characteristic features of their key components are considered as applied to corrosion inhibition, including datasets, response properties, molecular descriptors, machine learning methods, and structure-property models. It is shown that the most important factors determining their choice and application features are: (1) the small or very small size of datasets, (2) the mechanism of corrosion inhibition associated with the adsorption of inhibitor molecules on the metal surface, and (3) multifactorial conditioning and noisiness of response property. On this basis, the application of machine learning to the inhibition of corrosion of materials based on iron, aluminum, and magnesium is considered. The main trends in the development of QSPR and related data-driven modeling of corrosion inhibition are discussed, the shortcomings and common errors are considered, and the prospects for their further development are outlined.

Tyrosine Kinase Inhibitor Induced Proteinuria - A Review.

Tyrosine Kinase inhibitor (TKI) is a class of drugs that interfere with protein kinases' signal transduction pathways through an array of inhibitory mechanisms. Tyrosine kinases (TK) have an inevitable role in downstream signal transduction and the proliferation of tumour cells. Hence, tyrosine kinase inhibitors (TKIs) are frequently employed as anti-neoplastic agents in the treatment of colon, breast, kidney, and lung cancers. They can be used as single or combination therapy with other targeted therapies. It is understood that TKIs pose a risk of developing proteinuria in some patients as it can primarily result in dysfunction of the split diaphragm, constriction or blockage of capillary lumens mediated by the basement membrane, acute interstitial nephritis, or acute tubular necrosis. This paper reviews the mechanism of action of TKIs, the pathophysiological mechanism of TKI-induced proteinuria, and its management Fig. 1.

The Effect of Item Strength on Retrieval-Induced Forgetting in Social Interaction.

Retrieval-induced forgetting (RIF) refers to the phenomenon in which people retrieve information, but forget related information. RIF also occurs when people interact with each other. In social interactions, information recalled by the speaker can lead the listener to forget related information, a phenomenon known as socially shared retrieval-induced forgetting (SS-RIF). How does SS-RIF occur? Does it have similar mechanisms to RIF? By observing SS-RIF and RIF with different item strengths, this study investigated the mechanisms of SS-RIF. Item strength was manipulated based on exemplar taxonomic frequency, with high-frequency exemplars designated as strong items and low-frequency exemplars as weak. Experiment 1 found that only strong items exhibited SS-RIF and RIF, while weak items did not exhibit either SS-RIF or RIF. In Experiment 2, participants were asked to restudy the materials, and only the strong items still exhibited SS-RIF and RIF. Additionally, the magnitude of SS-RIF observed in Experiment 2 was similar to that observed in Experiment 1, as well as the performance on RIF. The findings of this study provide evidence for the inhibition mechanism of both SS-RIF and RIF, indicating a shared underlying mechanism.

Performance and mechanism of triethanolamine-triisopropanolamine corrosion inhibitor to deterioration of reinforced concrete under the coupling effect of freeze-thaw cycles and chloride attack

The purpose of this study is to propose an efficient and economical organic triethanolamine-triisopropanolamine corrosion inhibitor (OTTCI) to reduce the corrosion of steel in reinforced concrete. The influence of OTTCI on corrosion of steel in reinforced concrete under the coupling effect of freeze-thaw cycles and chloride attack (FTCs-CA) were characterized by electrochemical impedance spectroscopy (EIS), dynamic electrode potential (PDP), mechanical properties (mass loss rate (M), compressive strength (fn) and relative dynamic elastic modulus value (Pi)), capillary water absorption (CWA), bubble spacing coefficient (BSC) and scanning electron microscope (SEM). The inhibition mechanism of OTTCI was also analyzed and summarized. The results displayed that the dosage of OTTCI delayed the degradation of reinforced concrete under FTCs-CA. After 150 cycles, the M value of specimens with 1.0 % OTTCI reduced by 66.31 % compared to that of specimens without OTTCI, the Pi value increased by 51.9 %, and the polarization resistance and corrosion inhibition efficiency reached 2744.19 Ω cm2 and 92.88 %, respectively. In addition, OTTCI significantly reduced the CWA value and porosity. After 150 cycles, the CWA and porosity with 1.0 % OTTCI decreased by 60.1 % and 54.54 % respectively. The capillary water absorption coefficient increased linearly with the increase of FTCs-CA. SEM tests illustrated that OTTCI inhibited the development of internal cracks and macropores in concrete and promoted the formation of hydrated calcium silicate gels and calcite. The application of this study not only provides a new method to alleviate the deterioration of reinforced concrete, but also offers theoretical and technical support for further investigate on the deterioration characteristics of reinforced concrete in harsh environments.

Identification of inhibitors of human ChaC1, a cytoplasmic glutathione degrading enzyme through high throughput screens in yeast.

The cytosolic glutathione-degrading enzyme, ChaC1, is highly up-regulated in several cancers, with the up-regulation correlating to poor prognosis. The ability to inhibit ChaC1 is therefore important in different pathophysiological situations, but is challenging owing to the high substrate Km of the enzyme. As no inhibitors of ChaC1 are known, in this study we have focussed on this goal. We have initially taken a computational approach where a systemic structure-based virtual screening was performed. However, none of the predicted hits proved to be effective inhibitors. Synthetic substrate analogs were also not inhibitory. As both these approaches targeted the active site, we shifted to developing two high-throughput, robust, yeast-based assays that were active site independent. A small molecule compound library was screened using an automated liquid handling system using these screens. The hits were further analyzed using in vitro assays. Among them, juglone, a naturally occurring naphthoquinone, completely inhibited ChaC1 activity with an IC50 of 8.7 µM. It was also effective against the ChaC2 enzyme. Kinetic studies indicated that the inhibition was not competitive with the substrate. Juglone is known to form adducts with glutathione and is also known to selectively inhibit enzymes by covalently binding to active site cysteine residues. However, juglone continued to inhibit a cysteine-free ChaC1 variant, indicating that it was acting through a novel mechanism. We evaluated different inhibitory mechanisms, and also analogues of juglone, and found plumbagin effective as an inhibitor. These compounds are the first inhibitor leads against the ChaC enzymes using a robust yeast screen.

Intrinsic functional connectivity of right dorsolateral prefrontal cortex and hippocampus subregions relates to emotional and sensory-perceptual properties of intrusive trauma memories.

Trauma-related intrusive memories (TR-IMs), unwanted and vivid, are core symptoms of posttraumatic stress disorder (PTSD). Prior research links voluntary TR-IM suppression to inhibitory control of the right dorsolateral prefrontal cortex (dlPFC) over the hippocampus (HPC). However, the potential relevance of tonic resting-state inhibition has not been examined, nor has the functional differentiation of the anterior and posterior hippocampus (aHPC/HPC). This study examined relationships of TR-IM frequency and properties with resting-state negative coupling between the right dlPFC and right aHPC/pHPC in trauma-exposed individuals with PTSD symptoms. Participants (N=109; 88 female) completed two weeks of ecological momentary assessments capturing TR-IM frequency and properties (intrusiveness, emotional intensity, vividness, visual properties, and reliving). Using 3T resting-state magnetic resonance imaging, participant-specific 4-mm spheres were placed at the right dlPFC voxel most anticorrelated with the right aHPC and pHPC. Quasi-Poisson and linear mixed-effects models assessed relationships of TR-IM frequency and properties with right dlPFC-right aHPC and pHPC anticorrelation. TR-IM emotional intensity was positively associated with right dlPFC-aHPC connectivity, while vividness and visual properties were linked to right dlPFC-pHPC connectivity. No significant associations were found between TR-IM frequency, intrusiveness, or reliving, and anticorrelation with either HPC subregion. This study provides novel insights into the neural correlates of TR-IMs, highlighting the relevance of intrinsic negative coupling between the right dlPFC and aHPC/pHPC to their emotional impact and perceptual properties. Further research on inhibitory mechanisms in this circuit could improve understanding of component processes of intrusive reexperiencing, a severe and treatment-refractory PTSD symptom.

Evaluation and Analysis of Traditional Chinese Medicine Treatment of Bovine Viral Diarrhea/Mucosal Disease Based on Network Pharmacology and In Vitro Studies

Background Bovine viral diarrhea/mucosal disease (BVD-MD) is widely distributed worldwide. The disease causes serious economic losses to animal husbandry every year. Finding targeted antiviral drugs proves to be an effective strategy. Purpose This study was based on network pharmacology and in vitro studies to analyze the potential of traditional Chinese medicine (TCM) in the treatment of BVD-MD. Methods The intersection targets between TCM and the disease were identified. Network topology analysis and protein–protein interaction (PPIs) networks were performed. Intersection targets were analyzed for gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) enrichment. The molecular docking and molecular dynamics simulation methods were used to reveal the degree of binding of core components to key target genes. Characterization of the anti-Bovine viral diarrhea virus (BVDV) effect of TCM by cytotoxicity and in vitro studies. Results The results revealed the selection of five key Chinese medicines, along with 206 targets associated with BVD-MD. The toll-like receptor, PI3K-AKT, and tumor necrosis factor (TNF) signaling pathways were closely related to the five TCMs. AKT1, EGFR, HSP90AA1, and MAPK1 had good binding with quercetin, the core component of Chinese medicine. Molecular dynamics analysis showed that quercetin exhibited complex stability with AKT1. In vitro studies have demonstrated that the inhibitory effect of quercetin on BVDV is mainly in the initial phase. Quercetin inhibited the expression of AKT1. Conclusion The mechanism of BVDV inhibition by the core Chinese medicines is closely related to MAPK1, AKT1, TNF, and HSP90AA1, with the reduction of AKT1 ultimately affecting viral expression.

A comparative study of the cryo-EM structures of Saccharomyces cerevisiae and human anaphase-promoting complex/cyclosome (APC/C)

The anaphase-promoting complex/cyclosome (APC/C) is a large multi-subunit E3 ubiquitin ligase that controls progression through the cell cycle by orchestrating the timely proteolysis of mitotic cyclins and other cell cycle regulatory proteins. Although structures of multiple human APC/C complexes have been extensively studied over the past decade, the Saccharomyces cerevisiae APC/C has been less extensively investigated. Here, we describe medium resolution structures of three S. cerevisiae APC/C complexes: unphosphorylated apo-APC/C and the ternary APC/CCDH1-substrate complex, and phosphorylated apo-APC/C. Whereas the overall architectures of human and S. cerevisiae APC/C are conserved, as well as the mechanism of CDH1 inhibition by CDK-phosphorylation, specific variations exist, including striking differences in the mechanism of coactivator-mediated stimulation of E2 binding, and the activation of APC/CCDC20 by phosphorylation. In contrast to human APC/C in which coactivator induces a conformational change of the catalytic module APC2:APC11 to allow E2 binding, in S. cerevisiae apo-APC/C the catalytic module is already positioned to bind E2. Furthermore, we find no evidence of a phospho-regulatable auto-inhibitory segment of APC1, that in the unphosphorylated human APC/C, sterically blocks the CDC20C-box binding site of APC8. Thus, although the functions of APC/C are conserved from S. cerevisiae to humans, molecular details relating to their regulatory mechanisms differ.

A comparative study of the cryo-EM structures of Saccharomyces cerevisiae and human anaphase-promoting complex/cyclosome (APC/C).

The anaphase-promoting complex/cyclosome (APC/C) is a large multi-subunit E3 ubiquitin ligase that controls progression through the cell cycle by orchestrating the timely proteolysis of mitotic cyclins and other cell cycle regulatory proteins. Although structures of multiple human APC/C complexes have been extensively studied over the past decade, the Saccharomyces cerevisiae APC/C has been less extensively investigated. Here, we describe medium resolution structures of three S. cerevisiae APC/C complexes: unphosphorylated apo-APC/C and the ternary APC/CCDH1-substrate complex, and phosphorylated apo-APC/C. Whereas the overall architectures of human and S. cerevisiae APC/C are conserved, as well as the mechanism of CDH1 inhibition by CDK-phosphorylation, specific variations exist, including striking differences in the mechanism of coactivator-mediated stimulation of E2 binding, and the activation of APC/CCDC20 by phosphorylation. In contrast to human APC/C in which coactivator induces a conformational change of the catalytic module APC2:APC11 to allow E2 binding, in S. cerevisiae apo-APC/C the catalytic module is already positioned to bind E2. Furthermore, we find no evidence of a phospho-regulatable auto-inhibitory segment of APC1, that in the unphosphorylated human APC/C, sterically blocks the CDC20C-box binding site of APC8. Thus, although the functions of APC/C are conserved from S. cerevisiae to humans, molecular details relating to their regulatory mechanisms differ.

Supplemental Material for Lexical Inhibition After Semantic Violations Recruits a Domain-General Inhibitory Control Mechanism

Supplemental Material for Lexical Inhibition After Semantic Violations Recruits a Domain-General Inhibitory Control Mechanism

Deeply insight into the inhibition mechanism of SO2 on mercury oxidation over Mn/CNT: A DFT study

Mn/CNT is a kind of low temperature catalyst, which can effectively remove elemental mercury from flue gas at low temperature, but its mercury removal ability was significantly inhibited by SO2. In this work, the inhibition mechanism of SO2 was investigated by first-principle calculation based on density functional theory. Three different surfaces of Mn/CNT were constructed: MnO/CNT, MnO2/CNT and Mn2O3/CNT, and the adsorption of Hg0 and SO2 on these three surfaces were studied. It suggests that adsorption energy of Hg0 on MnO/CNT is the highest, which is −2.42 eV. Combined with the electron partial density of states (PDOS) after adsorption, SO2 can compete with Hg0 for the same Mn active site on the catalyst surface during the adsorption process, and the adsorption capacity of Hg0 is weaker than that of SO2. Oxidation path of Hg0 to HgO on the surface of Mn/CNT indicates that the generation of HgO needs to cross at least two energy barriers, with energies of 0.552 eV and 1.25 eV, respectively. However, when Hg0 was oxidized to HgO and adsorbed on the surface of Mn/CNT, SO2 could reduce it to Hg0 again, generating SO3 to block elemental mercury oxidation.

Integration of distinct cortical inputs to primary and higher order inhibitory cells of the thalamus.

The necortex regulates its own sensory input in part through top-down inhibitory mechanisms. Descending corticothalamic projections drive GABAergic neurons of the thalamic reticular nucleus (TRN), which then control thalamocortical cells via inhibition. Neurons in sensory TRN are organized into primary and higher order (HO) subpopulations, with separate intrathalamic connections and distinct genetic and functional properties. Here, we investigated top-down neocortical control over primary and HO neurons of somatosensory TRN. Projections from layer 6 of somatosensory cortex evoked stronger and more state-dependent activity in primary than in HO TRN, driven by more robust synaptic inputs and potent T-type calcium currents. However, HO TRN received additional, physiologically distinct, inputs from layer 5 of S1 and motor cortex. Thus, in a departure from the canonical focused sensory layer 6 innervation characteristic of primary TRN, HO TRN integrates broadly from multiple corticothalamic systems, with unique state-dependence, extending the range of mechanisms for top-down control.

A potential biocontrol and growth-promoting agent Streptomyces luteoverticillatus B4 for managing cabbage Fusarium wilt and cucumber Alternaria leaf blight

Cabbage Fusarium wilt and cucumber Alternaria leaf blight are two widespread diseases caused by Fusarium oxysporum and Alternaria cucumerina that severely affect cabbage and cucumber output across the world. However, very few biocontrol actinomycete resources have been identified for these two diseases. An antagonistic actinomycete B4 was isolated and identified as Streptomyces luteoverticillatus. It is effective against a wide range of plant pathogens. The purpose of this study was to look into the inhibitory impact of S. luteoverticillatus B4 on F. oxysporum and A. cucumerina, as well as to create the theoretical groundwork and research technologies for the use of B4 as a biopesticide. It was found that B4 has the ability to detoxify organic phosphorus and produce siderophores, IAA, and glucoamylase. In the greenhouse pot test, B4 had a control efficiency of 56 % against F. oxysporum and 76 % against A. cucumerina. Further investigation into the inhibitory mechanism indicated that once the B4 fermentation broth operated on the two pathogens, their mycelial morphology was altered, and mycelial growth was suppressed, particularly for F. oxysporum. B4 could create volatile organic compounds that may have an inhibiting impact. In addition, B4 fermentation broth dramatically increased seed germination and seedling development in both cabbage and cucumber. S. luteoverticillatus B4 is a possible biocontrol agent that inhibits F. oxysporum and A. cucumerina while also encouraging cabbage and cucumber development.

High-Throughput Single-Particle Characterization of Aggregation Pathways and the Effects of Inhibitors for Large (Megadalton) Protein Oligomers.

Protein aggregation is involved in many human diseases, but characterizing the sizes and shapes of intermediate oligomers (∼10-100 nm) that are important to the formation of macroscale aggregates like amyloid fibrils is a significant analytical challenge. Here, charge detection mass spectrometry (CDMS) is used to characterize individual conformational states of bovine serum albumin oligomers with up to ∼225 molecules (15 MDa). Elongated, partially folded, and globular conformational families for each oligomer can be readily distinguished based on the extent of charging. The abundances of individual conformers vary with changes in the monomer concentration or by adding aggregation inhibitors, such as SDS, heparin, or MgCl2. These results show the potential of CDMS for investigating intermediate oligomers in protein aggregation processes that are important for understanding aggregate formation and inhibition mechanisms and could accelerate formulation buffer development to prevent the aggregation of biotherapeutics.

Investigation of ponatinib metabolism and drug-drug interactions with lycopene and shikonin in vitro and invivo

Ponatinib is approved for use in patients with chronic myeloid leukemia (CML) who are resistant to or intolerant to prior tyrosine kinase inhibitor (TKI) therapy. Given that ponatinib can induce significant cardiotoxicity when taken, and that most Chinese medicines have cardioprotective effects, it is possible to administer them in combination in clinic to alleviate adverse effects. The quantitative determination of ponatinib and its metabolite N-desmethyl ponatinib was optimized and fully verified by ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS). And the drug-drug interactions (DDI) of ponatinib with lycopene and shikonin, both in vivo and in vitro, were studied. The results of bioanalytical methodology showed that ponatinib and N-desmethyl ponatinib had good linearity in plasma samples, and their selectivity, accuracy, precision, stability, matrix effect and recovery were all satisfied with the need of quantitative analysis of samples. In animal experiments, compared with the control group, lycopene and shikonin significantly changed the pharmacokinetic parameters of ponatinib, including AUC(0-t), AUC(0-∞) and CLz/F, while having no effect on the pharmacokinetic parameters of N-desmethyl ponatinib. In vitro interaction studies indicated that lycopene showed mixed inhibition mechanism on ponatinib metabolism in both rat liver microsomes (RLM) and human liver microsomes (HLM). And, shikonin displayed mixed inhibition mechanism in RLM and competitive inhibition mechanism in HLM, respectively. In summary, the UPLC-MS/MS method can accurately and sensitively quantify ponatinib and N-desmethyl ponatinib, and provide further reference for clinical drug combination between ponatinib and lycopene or shikonin.

Preparation of PVA/EG-WG gel foam and its inhibition of coal spontaneous combustion

In order to solve the shortcomings of existing gel foam such as poor stability, low strength and weak water retention capacity, a novel gel foam was prepared. The optimal ratio of this gel foam was determined in this experiment, and its inhibition performance and inhibition mechanism were analyzed. The results showed that the gel foam had the optimal performance when the mass fractions of foaming agent, foam stabilizer, gelling agent, cross-linking agent, Polyvinyl alcohol (PVA) and Ethylene glycol (EG) were 0.8 %, 1 %, 8 %, 2.2 %, 3 % and 7 %. After the gel foam action, the peak CO content in the oxidation process of coal samples decreased by 56.17 %, the average inhibition rate increased by 18.67 %, and the activation energy before and after the dry cracking temperature increased by 3.08 kJ and 9.20 kJ. The characteristic temperature points were greatly improved compared with those of the raw coal, which effectively slowed down the exothermic rate of coal oxidation. Compared with the traditional gel foam, PVA/EG-WG gel foam can achieve the effect of coal spontaneous combustion inhibition by means of inhibition and oxygen isolation, cooling and chemical reaction, etc.

Influence of oxygen on the hydrogen storage performance of Zr2Fe: Mechanism, diffusion pathway and DFT calculations

Zr2Fe alloy exhibits the advantages of being tritiated water-free and easy to recover in the form of reversible metal hydrides, which make it an ideal material for the trapping of hydrogen isotopes. However, its practical application is significantly limited by its susceptibility to poisoning by impurity gases such as oxygen. While significant progress has been made in understanding the effects of oxygen on hydrogen adsorption, a microscopic-level explanation of this interaction is still lacking. In this work, we employed detailed density functional theory to investigate the microscopic interaction mechanism between O2 and Zr2Fe, as well as the impact on hydrogen adsorption, addressing a gap in the current understanding. Our results reveal that O2 dissociatively adsorbs at hollow sites on the Zr2Fe surface, with oxygen atoms forming strong bonds with Zr and Fe atoms. This interaction blocks key active sites, hindering hydrogen diffusion into the alloy’s interior, as confirmed by climbing-image nudged elastic band calculations. These findings provide new insights into the inhibition mechanism caused by oxygen, offering a deeper understanding for improving the hydrogen storage performance of Zr-based alloys.

Applied Investigation of Methyl, Ethyl, Propyl, and Butyl Mercaptan as Potential Poisons in the Gas Phase Polymerization Reaction of Propylene.

The polypropylene (PP) synthesis process is crucial in the plastics industry, requiring precise control as it directly impacts the catalytic activity and the final product's performance. This study investigates the effects of trace amounts of four different mercaptans on the polymerization of propylene using a fourth-generation Ziegler-Natta (ZN) catalyst. Various concentrations of these mercaptans were tested, and results showed that their presence significantly reduced the melt flow index (MFI) of the final PP. The most notable MFI decrease occurred at 37.17 ppm of propyl mercaptan and 52.60 ppm of butyl mercaptan. Methyl and ethyl mercaptan also reduced the MFI at lower concentrations, indicating that mercaptans act as inhibitors by slowing down the polymerization process and reducing the fluidity of molten PP. The highest MFI increase was observed at lower concentrations of each mercaptan, suggesting that smaller molecular inhibitors require less concentration. This trend was also seen in the catalyst's productivity, where lower concentrations of methyl mercaptan reduced PP production more effectively than higher concentrations of butyl mercaptan. Fourier transform infrared spectroscopy (FTIR) identified interactions between the mercaptans and the ZN catalyst. Computational analysis further supported these findings, providing insights into the molecular interactions and suggesting possible inhibition mechanisms that could impact the final properties of polypropylene.

2.6-Å resolution cryo-EM structure of a class Ia ribonucleotide reductase trapped with mechanism-based inhibitor N3CDP.

Several FDA-approved cancer drugs target human ribonucleotide reductase (RNR), a radical enzyme that produces the requisite deoxyribonucleotides for DNA biosynthesis and repair. Human RNR is a class Ia enzyme that requires radical transfer (RT) from a β2 subunit to an α2 subunit on every round of turnover. Long-range RT is both a remarkable feature and an Achilles heel, given that inhibitors can intercept the radical species. Here we present a cryogenic electron microscopy (cryo-EM) structure of the best studied class Ia RNR, the enzyme from E. coli , in which α2 and β2 subunits have been trapped together using a mechanism-based inhibitor. This structure provides insight into both the mechanism of RNR inhibition and the mechanism of long-range RT.