Timing of chronic subdural hematoma treatment affects middle meningeal artery embolization outcome.

Background: Chronic subdural hematoma (CSDH) is a condition that tends to recur frequently. Although middle meningeal artery embolization (MMAE) is an effective CSDH treatment, there is currently no consensus regarding the optimal timing for embolization. Methods: In this single-center and retrospective study, we reviewed 72 cases with 1st-time recurrent CSDH from January 2018 to July 2023 and identified those treated with MMAE to examine its effect and the impact of differences in the timing of treatment. Results: Of the 72 cases with CSDH recurrence for the 1st time (mean age: 80.4 ± 9.7 years; men: 62 [86.1%]; mean first recurrence interval: 33 ± 24 days), 27 (37.5%) experienced a second recurrence. The mean first recurrence interval was shorter in cases with a second recurrence compared to cured cases: 24.3 ± 18.6 versus 38.3 ± 25.6 days, respectively (P = 0.005). MMAE was performed in 17 (23.6%) cases (mean age: 82 ± 6.2 years; men: 14 [82.4%]). The mean time from initial surgical treatment to embolization was 52.4 ± 35.4 days, and the mean recurrence interval before MMAE was 24.9 ± 19.6 days. Six cases (35.3%) experienced post-embolization recurrence and required surgical treatment. The mean recurrence interval before MMAE was shorter in cases with recurrence after MMAE (15 ± 6.4 vs. 30 ± 22.1 days, P = 0.023). The time from initial surgical treatment to embolization was significantly shorter: 31.3 ± 12.8 versus 63.9 ± 38.9 days (P = 0.039). Conclusion: Cases with a short first recurrence interval were more likely to experience a second recurrence. Repeated recurrences within a short time increased the likelihood of post-embolization recurrence. MMAE performed early following the initial surgical treatment increased the recurrence risk.

Use of phase plate cryo-EM reveals conformation diversity of therapeutic IgG with 50 kDa Fab fragment resolved below 6 Å.

While cryogenic electron microscopy (cryo-EM) is fruitfully used for harvesting high-resolution structures of sizable macromolecules, its application to small or flexible proteins composed of small domains like immunoglobulin (IgG) remain challenging. Here, we applied single particle cryo-EM to Rituximab, a therapeutic IgG mediating anti-tumor toxicity, to explore its solution conformations. We found Rituximab molecules exhibited aggregates in cryo-EM specimens contrary to its solution behavior, and utilized a non-ionic detergent to successfully disperse them as isolated particles amenable to single particle analysis. As the detergent adversely reduced the protein-to-solvent contrast, we employed phase plate contrast to mitigate the impaired protein visibility. Assisted by phase plate imaging, we obtained a canonical three-arm IgG structure with other structures displaying variable arm densities co-existing in solution, affirming high flexibility of arm-connecting linkers. Furthermore, we showed phase plate imaging enables reliable structure determination of Fab to sub-nanometer resolution from ab initio, yielding a characteristic two-lobe structure that could be unambiguously docked with crystal structure. Our findings revealed conformation diversity of IgG and demonstrated phase plate was viable for cryo-EM analysis of small proteins without symmetry. This work helps extend cryo-EM boundaries, providing a valuable imaging and structural analysis framework for macromolecules with similar challenging features.

Lipid Nanoparticle with 1,2-Di-O-octadecenyl-3-trimethylammonium-propane as a Component Lipid Confers Potent Responses of Th1 Cells and Antibody against Vaccine Antigen.

Adjuvants are effective tools to enhance vaccine efficacy and control the type of immune responses such as antibody and T helper 1 (Th1)- or Th2-type responses. Several studies suggest that interferon (IFN)-γ-producing Th1 cells play a significant role against infections caused by intracellular bacteria and viruses; however, only a few adjuvants can induce a strong Th1-type immune response. Recently, several studies have shown that lipid nanoparticles (LNPs) can be used as vaccine adjuvants and that each LNP has a different adjuvant activity. In this study, we screened LNPs to develop an adjuvant that can induce Th1 cells and antibodies using a conventional influenza split vaccine (SV) as an antigen in mice. We observed that LNP with 1,2-di-O-octadecenyl-3-trimethylammonium-propane (DOTMA) as a component lipid (DOTMA-LNP) elicited robust SV-specific IgG1 and IgG2 responses compared with SV alone in mice and was as efficient as SV adjuvanted with other adjuvants in mice. Furthermore, DOTMA-LNPs induced robust IFN-γ-producing Th1 cells without inflammatory responses compared to those of other adjuvants, which conferred strong cross-protection in mice. We also demonstrated the high versatility of DOTMA-LNP as a Th1 cell-inducing vaccine adjuvant using vaccine antigens derived from severe acute respiratory syndrome coronavirus 2 and Streptococcus pneumoniae. Our findings suggest the potential of DOTMA-LNP as a safe and effective Th1 cell-inducing adjuvant and show that LNP formulations are potentially potent adjuvants to enhance the effectiveness of other subunit vaccines.

Community recommendations on cryoEM data archiving and validation.

In January 2020, a workshop was held at EMBL-EBI (Hinxton, UK) to discuss data requirements for the deposition and validation of cryoEM structures, with a focus on single-particle analysis. The meeting was attended by 47 experts in data processing, model building and refinement, validation, and archiving of such structures. This report describes the workshop's motivation and history, the topics discussed, and the resulting consensus recommendations. Some challenges for future methods-development efforts in this area are also highlighted, as is the implementation to date of some of the recommendations.

Community recommendations on cryoEM data archiving and validation: Outcomes of a wwPDB/EMDB workshop on cryoEM data management, deposition and validation.

In January 2020, a workshop was held at EMBL-EBI (Hinxton, UK) to discuss data requirements for deposition and validation of cryoEM structures, with a focus on single-particle analysis. The meeting was attended by 47 experts in data processing, model building and refinement, validation, and archiving of such structures. This report describes the workshop's motivation and history, the topics discussed, and consensus recommendations resulting from the workshop. Some challenges for future methods-development efforts in this area are also highlighted, as is the implementation to date of some of the recommendations.

The Prevalence and Characteristics of Symptomatic Uncomplicated Diverticular Disease Among Asian Patients With Unexplained Abdominal Symptoms.

Background/Aims: The precise incidence of symptomatic uncomplicated diverticular disease (SUDD) and its effects on the quality of life (QOL) remain unclear, particularly in Asian patients with right-sided SUDD. We assess the prevalence of SUDD and its impact on QOL in a real-world population. Methods: Five institutional cohorts of patients who received outpatient treatment for unexplained abdominal symptoms from January 15, 2020 to March 31, 2022, were included. All patients underwent colonoscopy. SUDD was defined as the presence of recurrent abdominal symptoms, particularly pain in the lower right or left quadrant lasting > 24 hours in patients with diverticulosis at the site of pain. The 36-item short-form health survey was used to assess QOL. Results: Diverticula were identified in 108 of 361 patients. Among these 108 patients, 31% had SUDD, which was right-sided in 39% of cases. Of the 50 patients with right-sided diverticula, 36% had SUDD, as did 15 of 35 patients with left-sided diverticula (43%). Among the 33 patients with SUDD, diverticula were right-sided, left-sided, and bilateral in 39%, 45%, and 15% of patients, respectively. Diarrhea was more frequent in the SUDD group than in the non-SUDD group. Patients with SUDD had significantly lower physical, mental, and role/social component scores than those without SUDD. Conclusions: It is important to recognize that patients with SUDD account for as high as 31% of outpatients with unexplained abdominal symptoms; these patients have diarrhea and a low QOL. The presence of right-sided SUDD was characteristic of Asian patients.

Enhancement of SARS-CoV-2 Infection via Crosslinking of Adjacent Spike Proteins by N-Terminal Domain-Targeting Antibodies.

The entry of SARS-CoV-2 into host cells is mediated by the interaction between the spike receptor-binding domain (RBD) and host angiotensin-converting enzyme 2 (ACE2). Certain human antibodies, which target the spike N-terminal domain (NTD) at a distant epitope from the host cell binding surface, have been found to augment ACE2 binding and enhance SARS-CoV-2 infection. Notably, these antibodies exert their effect independently of the antibody fragment crystallizable (Fc) region, distinguishing their mode of action from previously described antibody-dependent infection-enhancing (ADE) mechanisms. Building upon previous hypotheses and experimental evidence, we propose that these NTD-targeting infection-enhancing antibodies (NIEAs) achieve their effect through the crosslinking of neighboring spike proteins. In this study, we present refined structural models of NIEA fragment antigen-binding region (Fab)-NTD complexes, supported by molecular dynamics simulations and hydrogen-deuterium exchange mass spectrometry (HDX-MS). Furthermore, we provide direct evidence confirming the crosslinking of spike NTDs by NIEAs. Collectively, our findings advance our understanding of the molecular mechanisms underlying NIEAs and their impact on SARS-CoV-2 infection.

An Ionizable Lipid Material with a Vitamin E Scaffold as an mRNA Vaccine Platform for Efficient Cytotoxic T Cell Responses.

RNA vaccines based on lipid nanoparticles (LNPs) with in vitro transcribed mRNA (IVT-mRNA) encapsulated are now a currently successful but still evolving modality of vaccines. One of the advantages of RNA vaccines is their ability to induce CD8+ T-cell-mediated cellular immunity that is indispensable for excluding pathogen-infected cells or cancer cells from the body. In this study, we report on the development of LNPs with an enhanced capability for inducing cellular immunity by using an ionizable lipid with a vitamin E scaffold. An RNA vaccine that contained this ionizable lipid and an IVT-mRNA encoding a model antigen ovalbumin (OVA) induced OVA-specific cytotoxic T cell responses and showed an antitumor effect against an E.G7-OVA tumor model. Vaccination with the LNPs conferred protection against lethal infection by Toxoplasma gondii using its antigen TgPF. The vitamin E scaffold-dependent type I interferon response was important for effector CD8+ T cell differentiation induced by the mRNA-LNPs. Our findings also revealed that conventional dendritic cells (cDCs) were essential for achieving CD8+ T cell responses induced by the mRNA-LNPs, while the XCR1-positive subset of cDCs, cDC1 specialized for antigen cross-presentation, was not required. Consistently, the mRNA-LNPs were found to selectively transfect another subset of cDCs, cDC2 that had migrated from the skin to lymph nodes, where they could make vaccine-antigen-dependent contacts with CD8+ T cells. The findings indicate that the activation of innate immune signaling by the adjuvant activity of the vitamin E scaffold and the expression of antigens in cDC2 are important for subsequent antigen presentation and the establishment of antigen-specific immune responses.

Structural insights into the agonists binding and receptor selectivity of human histamine H4 receptor.

Histamine is a biogenic amine that participates in allergic and inflammatory processes by stimulating histamine receptors. The histamine H4 receptor (H4R) is a potential therapeutic target for chronic inflammatory diseases such as asthma and atopic dermatitis. Here, we show the cryo-electron microscopy structures of the H4R-Gq complex bound with an endogenous agonist histamine or the selective agonist imetit bound in the orthosteric binding pocket. The structures demonstrate binding mode of histamine agonists and that the subtype-selective agonist binding causes conformational changes in Phe3447.39, which, in turn, form the "aromatic slot". The results provide insights into the molecular underpinnings of the agonism of H4R and subtype selectivity of histamine receptors, and show that the H4R structures may be valuable in rational drug design of drugs targeting the H4R.

Coenzyme-binding pathway on glutamate dehydrogenase suggested from multiple-binding sites visualized by cryo-electron microscopy.

The structure of hexameric glutamate dehydrogenase (GDH) in the presence of the coenzyme nicotinamide adenine dinucleotide phosphate (NADP) was visualized using cryogenic transmission electron microscopy to investigate the ligand-binding pathways to the active site of the enzyme. Each subunit of GDH comprises one hexamer-forming core domain and one nucleotide-binding domain (NAD domain), which spontaneously opens and closes the active-site cleft situated between the two domains. In the presence of NADP, the potential map of GDH hexamer, assuming D3 symmetry, was determined at a resolution of 2.4 Å, but the NAD domain was blurred due to the conformational variety. After focused classification with respect to the NAD domain, the potential maps interpreted as NADP molecules appeared at five different sites in the active-site cleft. The subunits associated with NADP molecules were close to one of the four metastable conformations in the unliganded state. Three of the five binding sites suggested a pathway of NADP molecules to approach the active-site cleft for initiating the enzymatic reaction. The other two binding modes may rarely appear in the presence of glutamate, as demonstrated by the reaction kinetics. Based on the visualized structures and the results from the enzymatic kinetics, we discussed the binding modes of NADP to GDH in the absence and presence of glutamate.

Development of a 1:1-binding biparatopic anti-TNFR2 antagonist by reducing signaling activity through epitope selection.

Conventional bivalent antibodies against cell surface receptors often initiate unwanted signal transduction by crosslinking two antigen molecules. Biparatopic antibodies (BpAbs) bind to two different epitopes on the same antigen, thus altering crosslinking ability. In this study, we develop BpAbs against tumor necrosis factor receptor 2 (TNFR2), which is an attractive immune checkpoint target. Using different pairs of antibody variable regions specific to topographically distinct TNFR2 epitopes, we successfully regulate the size of BpAb-TNFR2 immunocomplexes to result in controlled agonistic activities. Our series of results indicate that the relative positions of the two epitopes recognized by the BpAb are critical for controlling its signaling activity. One particular antagonist, Bp109-92, binds TNFR2 in a 1:1 manner without unwanted signal transduction, and its structural basis is determined using cryo-electron microscopy. This antagonist suppresses the proliferation of regulatory T cells expressing TNFR2. Therefore, the BpAb format would be useful in designing specific and distinct antibody functions.

An inhaled ACE2 decoy confers protection against SARS-CoV-2 infection in preclinical models.

The Omicron variant continuously evolves under the humoral immune pressure exerted by vaccination and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, and the resulting Omicron subvariants display further immune evasion and antibody escape. An engineered angiotensin-converting enzyme 2 (ACE2) decoy composed of high-affinity ACE2 and an IgG1 Fc domain could offer an alternative modality to neutralize SARS-CoV-2. We previously reported its broad spectrum and therapeutic potential in rodent models. Here, we demonstrate that the engineered ACE2 decoy retains neutralization activity against Omicron subvariants, including the currently emerging XBB and BQ.1 strains, which completely evade antibodies currently in clinical use. SARS-CoV-2, under the suboptimal concentration of neutralizing drugs, generated SARS-CoV-2 mutants escaping wild-type ACE2 decoy and monoclonal antibodies, whereas no escape mutant emerged against the engineered ACE2 decoy. Furthermore, inhalation of aerosolized decoys improved the outcomes of rodents infected with SARS-CoV-2 at a 20-fold lower dose than that of intravenous administration. Last, the engineered ACE2 decoy exhibited therapeutic efficacy for cynomolgus macaques infected with SARS-CoV-2. These results indicate that this engineered ACE2 decoy represents a promising therapeutic strategy to overcome immune-evading SARS-CoV-2 variants and that liquid aerosol inhalation could be considered as a noninvasive approach to enhance the efficacy of COVID-19 treatments.

Sequential Gaze-Shifting Approach to Reconstruct Self-portrait and Daily Activities in Hemispatial Neglect After Stroke: A Case Report.

Objectives: The aim of this study was to demonstrate the use of a sequential gaze-shifting approach to complete a self-portrait in a patient with hemispatial neglect after stroke as a means of rehabilitation to restore skills to perform activities of daily living (ADL). Methods: This case report describes a 71-year-old amateur painter who presented with severe left hemispatial neglect after stroke. Initially, he drew self-portraits omitting the left side. Six months poststroke, the patient was able to complete well-composed self-portraits by sequentially shifting his gaze and intentionally directing his visual attention from the right non-neglected space to the left neglected space. Then the patient was instructed to repeatedly practice a serial movement of each ADL using this sequential gaze-shifting technique. Results: Seven months poststroke, the patient achieved independence in ADL such as dressing the upper body, grooming, eating, and toileting although moderate hemispatial neglect and hemiparesis were still present. Discussion: The effects of existing rehabilitation approaches can be difficult to generalize and apply to the performance of each individual ADL in patients with hemispatial neglect after stroke. Sequential gaze shifting may be a viable compensation strategy in directing attention to the neglected space and restoring the ability to perform each ADL.

Epoxidized graphene grid for highly efficient high-resolution cryoEM structural analysis.

Functionalization of graphene is one of the most important fundamental technologies in a wide variety of fields including industry and biochemistry. We have successfully achieved a novel oxidative modification of graphene using photoactivated ClO2· as a mild oxidant and confirmed the oxidized graphene grid is storable with its functionality for at least three months under N2 atmosphere. Subsequent chemical functionalization enabled us to develop an epoxidized graphene grid (EG-grid™), which effectively adsorbs protein particles for electron cryomicroscopy (cryoEM) image analysis. The EG-grid dramatically improved the particle density and orientation distribution. The density maps of GroEL and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) were reconstructed at 1.99 and 2.16 Å resolution from only 504 and 241 micrographs, respectively. A sample solution of 0.1 mg ml-1 was sufficient to reconstruct a 3.10 Å resolution map of SARS-CoV-2 spike protein from 1163 micrographs. The map resolutions of ß-galactosidase and apoferritin easily reached 1.81 Å and 1.29 Å resolution, respectively, indicating its atomic-resolution imaging capability. Thus, the EG-grid will be an extremely powerful tool for highly efficient high-resolution cryoEM structural analysis of biological macromolecules.

Filamentous structures in the cell envelope are associated with bacteroidetes gliding machinery.

Many bacteria belonging to the phylum Bacteroidetes move on solid surfaces, called gliding motility. In our previous study with the Bacteroidetes gliding bacterium Flavobacterium johnsoniae, we proposed a helical loop track model, where adhesive SprB filaments are propelled along a helical loop on the cell surface. In this study, we observed the gliding cell rotating counterclockwise about its axis when viewed from the rear to the advancing direction of the cell and revealed that one labeled SprB focus sometimes overtook and passed another SprB focus that was moving in the same direction. Several electron microscopic analyses revealed the presence of a possible multi-rail structure underneath the outer membrane, which was associated with SprB filaments and contained GldJ protein. These results provide insights into the mechanism of Bacteroidetes gliding motility, in which the SprB filaments are propelled along tracks that may form a multi-rail system underneath the outer membrane. The insights may give clues as to how the SprB filaments get their driving force.

Intravascularly infused extracellular matrix as a biomaterial for targeting and treating inflamed tissues.

Decellularized extracellular matrix in the form of patches and locally injected hydrogels has long been used as therapies in animal models of disease. Here we report the safety and feasibility of an intravascularly infused extracellular matrix as a biomaterial for the repair of tissue in animal models of acute myocardial infarction, traumatic brain injury and pulmonary arterial hypertension. The biomaterial consists of decellularized, enzymatically digested and fractionated ventricular myocardium, localizes to injured tissues by binding to leaky microvasculature, and is largely degraded in about 3 d. In rats and pigs with induced acute myocardial infarction followed by intracoronary infusion of the biomaterial, we observed substantially reduced left ventricular volumes and improved wall-motion scores, as well as differential expression of genes associated with tissue repair and inflammation. Delivering pro-healing extracellular matrix by intravascular infusion post injury may provide translational advantages for the healing of inflamed tissues 'from the inside out'.

Progress in spatial resolution of structural analysis by cryo-EM.

Since the Human Genome Project, drug discovery via structure-based drug design and development has significantly accelerated. Therefore, generating high-resolution structural information from biological macromolecules and macromolecular complexes, such as proteins and nucleic acids, is paramount in structural biology, medicine and the pharmaceutical industry. Recently, electron cryomicroscopy (cryo-EM) has undergone a technological revolution and attracted much attention in the structure-based drug discovery pipeline. This recognition is primarily due to its ability to analyze and reconstruct high-resolution structures of previously unattainable large target macromolecular complexes captured in various functional and dynamic states. Previously, cryo-EM was a niche method in the structure determination field, and research was limited to a small number of laboratories and produced low-resolution structures incomplete for detailed and unambiguous structural interpretation. However, with the development of new camera technology, software and computational algorithms that now seamlessly integrate these new developments, the achievable resolutions produced from cryo-EM-determined structures have dramatically improved. This has solidified cryo-EM as one of the main structural determination methods widely used in the field. In this review, we introduce the evolution of two essential techniques incorporated into the cryo-EM workflow-single particle analysis and tomography-focusing on achievable resolution and the technological innovations that have become indispensable tools for high-resolution reconstruction and structural analysis of biological macromolecules. Here, we also describe challenges and discuss future prospects that have fixed cryo-EM as a dominant feature in the landscape of high-resolution structure determination methods and the structure-based drug discovery pipeline.

The Relationship Between Quadriceps Femoris Muscle Function and MRI-Derived Water Diffusion and Adipose Tissue Measurements in Young Healthy Males.

BACKGROUND: Water diffusion and adipose tissue in a muscle can be evaluated by MRI. However, determining which quadriceps femoris muscle (QM) characteristics independently predict peak knee extension torque during maximum voluntary isometric contractions (MVICs), individual muscle activity during MVICs and sit-to-stand transitions is unknown. PURPOSE: To determine which QM characteristics predict knee extension muscle strength and individual muscle activity. STUDY TYPE: Prospective, cross-sectional. SUBJECTS: A total of 20 healthy males (aged 22-40 years) with a physical activity level <1 hour/week. FIELD STRENGTH/SEQUENCE: 1.5-T, diffusion-weighted fast spin-echo echo-planar imaging and T1-weighted fast spin-echo sequences. ASSESSMENT: The vastus medialis (VM), vastus lateralis (VL), rectus femoris (RF), and vastus intermedius were segmented in a single axial diffusion-weighted image and T1-weighted image at the right mid-thigh region. λ1-3 and fractional anisotropy (FA), and the percentage of intramuscular adipose tissue (IMAT) were measured. The knee extension peak force during MVICs was measured by a dynamometer, and the torque was calculated at the peak force × length. The ratios of the individual muscle activity to the total muscle (VM, VL, and RF) during MVICs and sit-to-stand transitions were assessed using surface electromyography. STATISTICAL TESTS: Regression analysis was conducted to identify the predictors of peak knee extension torque and of individual muscle activity ratios. A P value < 0.05 was considered statistically significant. RESULTS: The RF λ1 significantly predicted the peak knee extension torque (ß = -0.51). The IMAT percentage of the VM significantly predicted the VM muscle activity ratio during the MVIC and sit-to-stand transition (ß = -0.82 and ß = -0.61, respectively), whereas the ratio of the VM λ1 to the whole QM λ1 significantly predicted the VM muscle activity ratio during the sit-to-stand transitions (ß = 0.35 and ß = 0.46, respectively). DATA CONCLUSION: The RF λ1 may allow to estimate peak knee extension muscle torque, and the VM IMAT and λ1 may predict muscle activity in youth. EVIDENCE LEVEL: 3. TECHNICAL EFFICACY: Stage 3.

Isolation and structure of the fibril protein, a major component of the internal ribbon for Spiroplasma swimming.

Spiroplasma, which are known pathogens and commensals of arthropods and plants, are helical-shaped bacteria that lack a peptidoglycan layer. Spiroplasma swim by alternating between left- and right-handed helicity. Of note, this system is not related to flagellar motility, which is widespread in bacteria. A helical ribbon running along the inner side of the helical cell should be responsible for cell helicity and comprises the bacterial actin homolog, MreB, and a protein specific to Spiroplasma, fibril. Here, we isolated the ribbon and its major component, fibril filament, for electron microscopy (EM) analysis. Single-particle analysis of the fibril filaments using the negative-staining EM revealed a three-dimensional chain structure composed of rings with a size of 11 nm wide and 6 nm long, connected by a backbone cylinder with an 8.7 nm interval with a twist along the filament axis. This structure was verified through EM tomography of quick-freeze deep-etch replica sample, with a focus on its handedness. The handedness and pitch of the helix for the isolated ribbon and fibril filament agreed with those of the cell in the resting state. Structures corresponding to the alternative state were not identified. These results suggest that the helical cell structure is supported by fibril filaments; however, the helical switch is caused by the force generated by the MreB proteins. The isolation and structural outline of the fibril filaments provide crucial information for an in-depth clarification of the unique swimming mechanism of Spiroplasma.

Cryo-EM structures of the translocational binary toxin complex CDTa-bound CDTb-pore from Clostridioides difficile.

Some bacteria express a binary toxin translocation system, consisting of an enzymatic subunit and translocation pore, that delivers enzymes into host cells through endocytosis. The most clinically important bacterium with such a system is Clostridioides difficile (formerly Clostridium). The CDTa and CDTb proteins from its system represent important therapeutic targets. CDTb has been proposed to be a di-heptamer, but its physiological heptameric structure has not yet been reported. Here, we report the cryo-EM structure of CDTa bound to the CDTb-pore, which reveals that CDTa binding induces partial unfolding and tilting of the first CDTa α-helix. In the CDTb-pore, an NSS-loop exists in 'in' and 'out' conformations, suggesting its involvement in substrate translocation. Finally, 3D variability analysis revealed CDTa movements from a folded to an unfolded state. These dynamic structural information provide insights into drug design against hypervirulent C. difficile strains.