SARS-CoV-2 Main Protease Inhibitors That Leverage Unique Interactions with the Solvent Exposed S3 Site of the Enzyme.

The main protease (MPro) of SARS-CoV-2 is crucial for the virus's replication and pathogenicity. Its active site is characterized by four distinct pockets (S1, S2, S4, and S1-3') and a solvent-exposed S3 site for accommodating a protein substrate. During X-ray crystallographic analyses of MPro bound with dipeptide inhibitors containing a flexible N-terminal group, we often observed an unexpected binding mode. Contrary to the anticipated engagement with the deeper S4 pocket, the N-terminal group frequently assumed a twisted conformation, positioning it for interactions with the S3 site and the inhibitor component bound at the S1 pocket. Capitalizing on this observation, we engineered novel inhibitors to engage both S3 and S4 sites or to adopt a rigid conformation for selective S3 site binding. Several new inhibitors demonstrated high efficacy in MPro inhibition. Our findings underscore the importance of the S3 site's unique interactions in the design of future MPro inhibitors as potential COVID-19 therapeutics.

Quantitative imaging of loop extruders rebuilding interphase genome architecture after mitosis.

How cells establish the interphase genome organization after mitosis is incompletely understood. Using quantitative and super-resolution microscopy, we show that the transition from a Condensin to a Cohesin-based genome organization occurs dynamically over two hours. While a significant fraction of Condensins remains chromatin-bound until early G1, Cohesin-STAG1 and its boundary factor CTCF are rapidly imported into daughter nuclei in telophase, immediately bind chromosomes as individual complexes and are sufficient to build the first interphase TAD structures. By contrast, the more abundant Cohesin-STAG2 accumulates on chromosomes only gradually later in G1, is responsible for compaction inside TAD structures and forms paired complexes upon completed nuclear import. Our quantitative time-resolved mapping of mitotic and interphase loop extruders in single cells reveals that the nested loop architecture formed by sequential action of two Condensins in mitosis is seamlessly replaced by a less compact, but conceptually similar hierarchically nested loop architecture driven by sequential action of two Cohesins.

Four Generations of Volcano Plots for the Oxygen Evolution Reaction: Beyond Proton-Coupled Electron Transfer Steps?

ConspectusDue to its importance for electrolyzers or metal-air batteries for energy conversion or storage, there is huge interest in the development of high-performance materials for the oxygen evolution reaction (OER). Theoretical investigations have aided the search for active material motifs through the construction of volcano plots for the kinetically sluggish OER, which involves the transfer of four proton-electron pairs to form a single oxygen molecule. The theory-driven volcano approach has gained unprecedented popularity in the catalysis and energy communities, largely due to its simplicity, as adsorption free energies can be used to approximate the electrocatalytic activity by heuristic descriptors.In the last two decades, the binding-energy-based volcano method has witnessed a renaissance with special concepts being developed to incorporate missing factors into the analysis. To this end, this Account summarizes and discusses the different generations of volcano plots for the example of the OER. While first-generation methods relied on the assessment of the thermodynamic information for the OER reaction intermediates by means of scaling relations, the second and third generations developed strategies to include overpotential and kinetic effects into the analysis of activity trends. Finally, the fourth generation of volcano approaches allowed the incorporation of various mechanistic pathways into the volcano methodology, thus paving the path toward data- and mechanistic-driven volcano plots in electrocatalysis.Although the concept of volcano plots has been significantly expanded in recent years, further research activities are discussed by challenging one of the main paradigms of the volcano concept. To date, the evaluation of activity trends relies on the assumption of proton-coupled electron transfer steps (CPET), even though there is experimental evidence of sequential proton-electron transfer (SPET) steps. While the computational assessment of SPET for solid-state electrodes is ambitious, it is strongly suggested to comprehend their importance in energy conversion and storage processes, including the OER. This can be achieved by knowledge transfer from homogeneous to heterogeneous electrocatalysis and by focusing on the material class of single-atom catalysts in which the active center is well defined. The derived concept of how to analyze the importance of SPET for mechanistic pathways in the OER over solid-state electrodes could further shape our understanding of the proton-electron transfer steps at electrified solid/liquid interfaces, which is crucial for further progress toward sustainable energy and climate neutrality.

Associations between disordered eating, internalizing symptoms, and behavioral and neural correlates of response inhibition in preadolescence.

Response inhibition difficulties are reported in individuals with eating disorders (EDs), anxiety, and depression. Although ED symptoms and internalizing symptoms co-occur in preadolescence, there is limited research examining associations between these symptoms and response inhibition in this age group. This study is the first to investigate the associations between behavioral and neural markers of response inhibition, disordered eating (DE), and internalizing symptoms in a community sample of preadolescents. Forty-eight children (M age = 10.95 years, 56.3% male) completed a Go/NoGo task, whereas electroencephalography was recorded. Self-report measures of DE and internalizing symptoms were collected. Higher levels of anxiety and depression were associated with neural markers of suboptimal response inhibition (attenuated P3NoGo amplitudes) in preadolescence. In contrast, higher levels of depression were associated with greater response inhibition at a behavioral level. These findings suggest internalizing symptoms in preadolescence are associated with P3-indexed difficulties in evaluation and monitoring, but these are not sufficient to disrupt behavioral performance on a response inhibition task. This pattern may reflect engagement of compensatory processes to support task performance. DE was not significantly associated with response inhibition, suggesting that difficulties in response inhibition may only be reliably observed in more chronic and severe DE and ED presentations.

Azapeptides with unique covalent warheads as SARS-CoV-2 main protease inhibitors.

The main protease (MPro) of SARS-CoV-2, the causative agent of COVID-19, is a pivotal nonstructural protein critical for viral replication and pathogenesis. Its protease function relies on three active site pockets for substrate recognition and a catalytic cysteine for enzymatic activity. To develop potential SARS-CoV-2 antivirals, we successfully synthesized a diverse range of azapeptide inhibitors with various covalent warheads to target MPro's catalytic cysteine. Our characterization identified potent MPro inhibitors, including MPI89 that features an aza-2,2-dichloroacetyl warhead with a remarkable EC50 value of 10 nM against SARS-CoV-2 infection in ACE2+ A549 cells and a selective index of 875. MPI89 is also remarkably selective and shows no potency against SARS-CoV-2 papain-like protease and several human proteases. Crystallography analyses demonstrated that these inhibitors covalently engaged the catalytic cysteine and used the aza-amide carbonyl oxygen to bind to the oxyanion hole. MPI89 stands as one of the most potent MPro inhibitors, suggesting the potential for further exploration of azapeptides and the aza-2,2-dichloroacetyl warhead for developing effective therapeutics against COVID-19.

Why efficient bifunctional hydrogen electrocatalysis requires a change in the reaction mechanism.

Hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) are both two-electron processes that culminate in the formation or consumption of gaseous hydrogen in an electrolyzer or a fuel cell, respectively. Unitized regenerative proton exchange membrane fuel cells merge these two functionalities into one device, allowing to switch between the two modes of operation. This prompts the quest for efficient bifunctional electrode materials catalyzing the HER and HOR with reasonable reaction rates at low overpotentials. In the present study using a data-driven framework, we identify a general criterion for efficient bifunctional performance in the hydrogen electrocatalysis, which refers to a change in the reaction mechanism when switching from cathodic to anodic working conditions. The obtained insight can be used in future studies based on density functional theory to pave the design of efficient HER and HOR catalysts by a dedicated consideration of the kinetics in the analysis of reaction mechanisms.

Importance of the Walden Inversion for the Activity Volcano Plot of Oxygen Evolution.

Since the birth of the computational hydrogen electrode approach, it is considered that activity trends of electrocatalysts in a homologous series can be quantified by the construction of volcano plots. This method aims to steer materials discovery by the identification of catalysts with an improved reaction kinetics, though evaluated by means of thermodynamic descriptors. The conventional approach for the volcano plot of the oxygen evolution reaction (OER) relies on the assumption of the mononuclear mechanism, comprising the * OH, * O, and * OOH intermediates. In the present manuscript, two new mechanistic pathways, comprising the idea of the Walden inversion in that bond-breaking and bond-making occurs simultaneously, are factored into a potential-dependent OER activity volcano plot. Surprisingly, it turns out that the Walden inversion plays an important role since the activity volcano is governed by mechanistic pathways comprising Walden steps rather than by the traditionally assumed reaction mechanisms under typical OER conditions.

A Systematic Survey of Reversibly Covalent Dipeptidyl Inhibitors of the SARS-CoV-2 Main Protease.

SARS-CoV-2, the COVID-19 pathogen, relies on its main protease (MPro) for replication and pathogenesis. MPro is a demonstrated target for the development of antivirals for SARS-CoV-2. Past studies have systematically explored tripeptidyl inhibitors such as nirmatrelvir as MPro inhibitors. However, dipeptidyl inhibitors especially those with a spiro residue at their P2 position have not been systematically investigated. In this work, we synthesized about 30 dipeptidyl MPro inhibitors and characterized them on enzymatic inhibition potency, structures of their complexes with MPro, cellular MPro inhibition potency, antiviral potency, cytotoxicity, and in vitro metabolic stability. Our results indicated that MPro has a flexible S2 pocket to accommodate inhibitors with a large P2 residue and revealed that dipeptidyl inhibitors with a large P2 spiro residue such as (S)-2-azaspiro [4,4]nonane-3-carboxylate and (S)-2-azaspiro[4,5]decane-3-carboxylate have favorable characteristics. One compound, MPI60, containing a P2 (S)-2-azaspiro[4,4]nonane-3-carboxylate displayed high antiviral potency, low cellular cytotoxicity, and high in vitro metabolic stability.

Importance of broken geometric symmetry of single-atom Pt sites for efficient electrocatalysis.

Platinum single-atom catalysts hold promise as a new frontier in heterogeneous electrocatalysis. However, the exact chemical nature of active Pt sites is highly elusive, arousing many hypotheses to compensate for the significant discrepancies between experiments and theories. Here, we identify the stabilization of low-coordinated PtII species on carbon-based Pt single-atom catalysts, which have rarely been found as reaction intermediates of homogeneous PtII catalysts but have often been proposed as catalytic sites for Pt single-atom catalysts from theory. Advanced online spectroscopic studies reveal multiple identities of PtII moieties on the single-atom catalysts beyond ideally four-coordinated PtII-N4. Notably, decreasing Pt content to 0.15 wt.% enables the differentiation of low-coordinated PtII species from the four-coordinated ones, demonstrating their critical role in the chlorine evolution reaction. This study may afford general guidelines for achieving a high electrocatalytic performance of carbon-based single-atom catalysts based on other d8 metal ions.

An Azapeptide Platform in Conjunction with Covalent Warheads to Uncover High-Potency Inhibitors for SARS-CoV-2 Main Protease.

Main protease (M Pro ) of SARS-CoV-2, the viral pathogen of COVID-19, is a crucial nonstructural protein that plays a vital role in the replication and pathogenesis of the virus. Its protease function relies on three active site pockets to recognize P1, P2, and P4 amino acid residues in a substrate and a catalytic cysteine residue for catalysis. By converting the P1 Cα atom in an M Pro substrate to nitrogen, we showed that a large variety of azapeptide inhibitors with covalent warheads targeting the M Pro catalytic cysteine could be easily synthesized. Through the characterization of these inhibitors, we identified several highly potent M Pro inhibitors. Specifically, one inhibitor, MPI89 that contained an aza-2,2-dichloroacetyl warhead, displayed a 10 nM EC 50 value in inhibiting SARS-CoV-2 from infecting ACE2 + A549 cells and a selectivity index of 875. The crystallography analyses of M Pro bound with 6 inhibitors, including MPI89, revealed that inhibitors used their covalent warheads to covalently engage the catalytic cysteine and the aza-amide carbonyl oxygen to bind to the oxyanion hole. MPI89 represents one of the most potent M Pro inhibitors developed so far, suggesting that further exploration of the azapeptide platform and the aza-2,2-dichloroacetyl warhead is needed for the development of potent inhibitors for the SARS-CoV-2 M Pro as therapeutics for COVID-19.

On the mechanistic complexity of oxygen evolution: potential-dependent switching of the mechanism at the volcano apex.

The anodic four-electron oxygen evolution reaction (OER) corresponds to the limiting process in acidic or alkaline electrolyzers to produce gaseous hydrogen at the cathode of the device. In the last decade, tremendous efforts have been dedicated to the identification of active OER materials by electronic structure calculations in the density functional theory approximation. Most of these works rely on the assumption that the mononuclear mechanism, comprising the *OH, *O, and *OOH intermediates, is operative under OER conditions, and that a single elementary reaction step (most likely *OOH formation) governs the kinetics. In the present manuscript, six different OER mechanisms are analyzed, and potential-dependent volcano curves are constructed to comprehend the electrocatalytic activity of these pathways in the approximation of the descriptor Gmax(U), a potential-dependent activity measure based on the notion of the free-energy span model. While the mononuclear description mainly describes the legs of the volcano plot, corresponding to electrocatalysts with low intrinsic activity, it is demonstrated that the preferred pathway at the volcano apex is a strong function of the applied electrode potential. The observed mechanistic complexity including a switch of the favored pathway with increasing overpotential sets previous investigations aiming at the identification of reaction mechanisms and limiting steps into question since the entire breadth of OER pathways was not accounted for. A prerequisite for future atomic-scale studies on highly active OER catalysts refers to the evaluation of several mechanistic pathways so that neither important mechanistic features are overlooked nor limiting steps are incorrectly determined.

Steering Selectivity in the Four-Electron and Two-Electron Oxygen Reduction Reactions: On the Importance of the Volcano Slope.

In the last decade, trends for competing electrocatalytic processes have been largely captured by volcano plots, which can be constructed by the analysis of adsorption free energies as derived from electronic structure theory in the density functional theory approximation. One prototypical example refers to the four-electron and two-electron oxygen reduction reactions (ORRs), resulting in the formation of water and hydrogen peroxide, respectively. The conventional thermodynamic volcano curve illustrates that the four-electron and two-electron ORRs reveal the same slopes at the volcano legs. This finding is related to two facts, namely, that only a single mechanistic description is considered in the model, and electrocatalytic activity is assessed by the concept of the limiting potential, a simple thermodynamic descriptor evaluated at the equilibrium potential. In the present contribution, the selectivity challenge of the four-electron and two-electron ORRs is analyzed, thereby accounting for two major expansions. First, different reaction mechanisms are included into the analysis, and second, G max(U), a potential-dependent activity measure that factors overpotential and kinetic effects into the evaluation of adsorption free energies, is applied for approximation of electrocatalytic activity. It is illustrated that the slope of the four-electron ORR is not constant at the volcano legs but rather is prone to change as soon as another mechanistic pathway is energetically preferred or another elementary step becomes the limiting one. Due to the varying slope of the four-electron ORR volcano, a trade-off between activity and selectivity for hydrogen peroxide formation is observed. It is demonstrated that the two-electron ORR is energetically preferred at the left and right volcano legs, thus opening a new strategy for the selective formation of H2O2 by an environmentally benign route.

Materials Screening by the Descriptor G max(η): The Free-Energy Span Model in Electrocatalysis.

To move from fossil-based energy resources to a society based on renewables, electrode materials free of precious noble metals are required to efficiently catalyze electrochemical processes in fuel cells, batteries, or electrolyzers. Materials screening operating at minimal computational cost is a powerful method to assess the performance of potential electrode compositions based on heuristic concepts. While the thermodynamic overpotential in combination with the volcano concept refers to the most popular descriptor-based analysis in the literature, this notion cannot reproduce experimental trends reasonably well. About two years ago, the concept of G max(η), based on the idea of the free-energy span model, has been proposed as a universal approach for the screening of electrocatalysts. In contrast to other available descriptor-based methods, G max(η) factors overpotential and kinetic effects by a dedicated evacuation scheme of adsorption free energies into an analysis of trends. In the present perspective, we discuss the application of G max(η) to different electrocatalytic processes, including the oxygen evolution and reduction reactions, the nitrogen reduction reaction, and the selectivity problem of the competing oxygen evolution and peroxide formation reactions, and we outline the advantages of this screening approach over previous investigations.

A Systematic Survey of Reversibly Covalent Dipeptidyl Inhibitors of the SARS-CoV-2 Main Protease.

SARS-CoV-2 is the coronavirus pathogen of the currently prevailing COVID-19 pandemic. It relies on its main protease (M Pro ) for replication and pathogenesis. M Pro is a demonstrated target for the development of antivirals for SARS-CoV-2. Past studies have systematically explored tripeptidyl inhibitors such as nirmatrelvir as M Pro inhibitors. However, dipeptidyl inhibitors especially those with a spiro residue at their P2 position have not been systematically investigated. In this work, we synthesized about 30 reversibly covalent dipeptidyl M Pro inhibitors and characterized them on in vitro enzymatic inhibition potency, structures of their complexes with M Pro , cellular M Pro inhibition potency, antiviral potency, cytotoxicity, and in vitro metabolic stability. Our results indicated that M Pro has a flexible S2 pocket that accommodates dipeptidyl inhibitors with a large P2 residue and revealed that dipeptidyl inhibitors with a large P2 spiro residue such as ( S )-2-azaspiro[4,4]nonane-3-carboxylate and ( S )-2-azaspiro[4,5]decane-3-carboxylate have optimal characteristics. One compound MPI60 containing a P2 ( S )-2-azaspiro[4,4]nonane-3-carboxylate displayed high antiviral potency, low cellular cytotoxicity, and high in vitro metabolic stability and can be potentially advanced to further preclinical tests.

A Novel Y-Shaped, S-O-N-O-S-Bridged Cross-Link between Three Residues C22, C44, and K61 Is Frequently Observed in the SARS-CoV-2 Main Protease.

As the COVID-19 pathogen, SARS-CoV-2 relies on its main protease (MPro) for pathogenesis and replication. During crystallographic analyses of MPro crystals that were exposed to the air, a uniquely Y-shaped, S-O-N-O-S-bridged post-translational cross-link that connects three residues C22, C44, and K61 at their side chains was frequently observed. As a novel covalent modification, this cross-link serves potentially as a redox switch to regulate the catalytic activity of MPro, a demonstrated drug target of COVID-19. The formation of this linkage leads to a much more open active site that can potentially be targeted for the development of novel SARS-CoV-2 antivirals. The structural rearrangement of MPro by this cross-link indicates that small molecules that lock MPro in the cross-linked form can potentially be used with other active-site-targeting molecules such as paxlovid for synergistic effects in inhibiting SARS-CoV-2 viral replication.

Mechanical Properties of 3D-Printed Liquid Crystalline Polymers with Low and High Melting Temperatures.

Additive manufacturing allows for the production of complex components using various types of materials such as plastics, metals and ceramics without the need for molding tools. In the field of high-performance polymers, semi-crystalline polymers such as polyetheretherketone (PEEK) or amorphous polymers such as polyetherimide (PEI) are already successfully applied. Contrary to semi-crystalline and amorphous polymers, thermotropic liquid crystalline polymers (LCPs) do not change into an isotropic liquid during melting. Instead, they possess anisotropic properties in their liquid phase. Within the scope of this work, this special group of polymers was investigated with regard to its suitability for processing by means of fused filament fabrication. Using an LCP with a low melting temperature of around 280 °C is compared to processing an LCP that exhibits a high melting temperature around 330 °C. In doing so, it was revealed that the achievable mechanical properties strongly depend on the process parameters such as the direction of deposition, printing temperature, printing speed and layer height. At a layer height of 0.10 mm, a Young's modulus of 27.3 GPa was achieved. Moreover, by employing an annealing step after the printing process, the tensile strength could be increased up to 406 MPa at a layer height of 0.15 mm. Regarding the general suitability for FFF as well as the achieved uniaxial mechanical properties, the LCP with a low melting temperature was advantageous compared to the LCP with a high melting temperature.

Phage-assisted, active site-directed ligand evolution of a potent and selective histone deacetylase 8 inhibitor.

Phage-assisted, active site-directed ligand evolution (PADLE) is a recently developed technique that uses an amber codon-encoded noncanonical amino acid (ncAA) as an anchor to direct phage-displayed peptides to a target for an enhanced ligand identification process. 2-Amino-8-oxodecanoic acid (Aoda) is a ketone-containing ncAA residue in the macrocyclic peptide natural product apicidin that is a pan-inhibitor of Zn2+ -dependent histone deacetylases (HDACs). Its ketone serves as an anchoring point to coordinate the catalytic zinc ion in HDACs. Using a previously evolved N𝜀 -acetyl-lysyl-tRNA synthetase in combination with tRNAPyl , we showed that Aoda was efficiently incorporated into proteins in Escherichia coli by amber suppression. By propagating an amber codon-obligate phagemid library in E. coli encoding Aoda, we generated an Aoda-containing phage-displayed peptide library. Using this library to conduct PADLE against HDAC8 revealed a 7-mer peptide GH8P01F1 with Aoda-flanking amino acid residues that matched existing peptide sequences in identified HDAC8 substrates. Switching Aoda in GH8P01F1 to a more Zn2+ -chelating ncAA S-2-amino-8-hydroxyamino-8-oxooctanoic acid (Asuha) led to an extremely potent compound GH8HA01, which has an HDAC8-inhibition Ki value of 0.67 nM. GH8HA01 and its 5-mer truncation analogue Ac-GH8HA01Δ1Δ7 that has an HDAC8-inhibition Ki value of 0.31 nM are two of the most potent HDAC8 inhibitors that have been developed. Furthermore, both are highly selective against HDAC8 compared with other HDACs tested, demonstrating the great potential of using PADLE to identify highly potent and selective ligands for targets with conserved active sites among homologues.

Prognostic value of primary tumor sidedness in patients with non-metastatic IBD related CRC - Is it the exception to the rule?

BACKGROUND: Although primary tumor sidedness (PTS) has a known prognostic role in sporadic colorectal cancer (CRC), its role in Inflammatory Bowel Disease related CRC (IBD-CRC) is largely unknown. Thus, we aimed to evaluate the prognostic role of PTS in patients with IBD-CRC. METHODS: All eligible patients with surgically treated, non-metastatic IBD-CRC were retrospectively identified from institutional databases at ten European and Asian academic centers. Long term endpoints included recurrence-free (RFS) and overall survival (OS). Multivariable Cox proportional hazard regression as well as propensity score analyses were performed to evaluate whether PTS was significantly associated with RFS and OS. RESULTS: A total of 213 patients were included in the analysis, of which 32.4% had right-sided (RS) tumors and 67.6% had left-sided (LS) tumors. PTS was not associated with OS and RFS even on univariable analysis (5-year OS for RS vs LS tumors was 68.0% vs 77.3%, respectively, p = 0.31; 5-year RFS for RS vs LS tumors was 62.8% vs 65.4%, respectively, p = 0.51). Similarly, PTS was not associated with OS and RFS on propensity score matched analysis (5-year OS for RS vs LS tumors was 82.9% vs 91.3%, p = 0.79; 5-year RFS for RS vs LS tumors was 85.1% vs 81.5%, p = 0.69). These results were maintained when OS and RFS were calculated in patients with RS vs LS tumors after excluding patients with rectal tumors (5-year OS for RS vs LS tumors was 68.0% vs 77.2%, respectively, p = 0.38; 5-year RFS for RS vs LS tumors was 62.8% vs 59.2%, respectively, p = 0.98). CONCLUSIONS: In contrast to sporadic CRC, PTS does not appear to have a prognostic role in IBD-CRC.

Neural synchrony in cortical networks: mechanisms and implications for neural information processing and coding.

Synchronization of neuronal discharges on the millisecond scale has long been recognized as a prevalent and functionally important attribute of neural activity. In this article, I review classical concepts and corresponding evidence of the mechanisms that govern the synchronization of distributed discharges in cortical networks and relate those mechanisms to their possible roles in coding and cognitive functions. To accommodate the need for a selective, directed synchronization of cells, I propose that synchronous firing of distributed neurons is a natural consequence of spike-timing-dependent plasticity (STDP) that associates cells repetitively receiving temporally coherent input: the "synchrony through synaptic plasticity" hypothesis. Neurons that are excited by a repeated sequence of synaptic inputs may learn to selectively respond to the onset of this sequence through synaptic plasticity. Multiple neurons receiving coherent input could thus actively synchronize their firing by learning to selectively respond at corresponding temporal positions. The hypothesis makes several predictions: first, the position of the cells in the network, as well as the source of their input signals, would be irrelevant as long as their input signals arrive simultaneously; second, repeating discharge patterns should get compressed until all or some part of the signals are synchronized; and third, this compression should be accompanied by a sparsening of signals. In this way, selective groups of cells could emerge that would respond to some recurring event with synchronous firing. Such a learned response pattern could further be modulated by synchronous network oscillations that provide a dynamic, flexible context for the synaptic integration of distributed signals. I conclude by suggesting experimental approaches to further test this new hypothesis.

Repurposing Halicin as a potent covalent inhibitor for the SARS-CoV-2 main protease.

The rapid spread of COVID-19 has caused a worldwide public health crisis. For prompt and effective development of antivirals for SARS-CoV-2, the pathogen of COVID-19, drug repurposing has been broadly conducted by targeting the main protease (MPro), a key enzyme responsible for the replication of virus inside the host. In this study, we evaluate the inhibition potency of a nitrothiazole-containing drug, halicin, and reveal its reaction and interaction mechanism with MPro. The in vitro potency test shows that halicin inhibits the activity of MPro an IC50 of 181.7 â€‹nM. Native mass spectrometry and X-ray crystallography studies clearly indicate that the nitrothiazole fragment of halicin covalently binds to the catalytic cysteine C145 of MPro. Interaction and conformational changes inside the active site of MPro suggest a favorable nucleophilic aromatic substitution reaction mechanism between MPro C145 and halicin, explaining the high inhibition potency of halicin towards MPro.