Host Cell Interactions Research Articles

From host individual traits to community structure and composition: Bartonella infection insights

BackgroundPhylogeny, combined with trait-based measures, offers insights into parasite sharing among hosts. However, the specific traits that mediate transmission and the aspects of host community diversity that most effectively explain parasite infection rates remain unclear, even for the Bartonella genus, a vector-borne bacteria that causes persistent blood infections in vertebrates.MethodsThis study investigated the association between rodent host traits and Bartonella infection, as well as how rodent community diversity affects the odds of infection in the Atlantic Forest, using generalized linear models. Additionally, we assessed how host traits and phylogenetic similarities influence Bartonella infection among mammal species in Brazil. To this end, rodents were sampled from ten municipalities in Rio de Janeiro, southeastern Brazil. Then, we calculated several diversity indices for each community, including Rényi’s diversity profiles, Fisher’s alpha, Rao’s quadratic entropy (RaoQ), Functional Diversity (FDis), Functional Richness (FRic), and Functional Evenness (FEve). Finally, we compiled a network encompassing all known interactions between mammal species and Bartonella lineages recorded in Brazil.ResultsWe found no significant relationship between diversity indices and the odds of Bartonella infection in rodent communities. Furthermore, there was no statistical support for the influence of individual-level traits (e.g., body length, sex, and age) or species-level ecological traits (e.g., locomotor habitat, dietary guild, and activity period) on Bartonella infection in rodents. A country-scale analysis, considering all mammal species, revealed no effect of host traits or phylogeny on Bartonella infection.ConclusionsThis study highlighted wild mammals that share Bartonella lineages with livestock, synanthropic, and domestic animals, underscoring the complexity of their maintenance cycle within the One Health framework. A key question arising from our findings is whether molecular host–cell interactions outweigh host body mass and ecological traits in influencing Bartonella infection, potentially opening new avenues for understanding host–parasite relationships and infection ecology.Graphical

Decoding host cell interaction– and fluconazole-induced metabolic alterations and drug resistance in Candida auris

ABSTRACT Candida auris is an emerging drug-resistant pathogen associated with high mortality rates. This study aimed to explore the metabolic alterations and associated pathogenesis and drug resistance in fluconazole-treated Candida auris–host cell interaction. Compared with controls, secreted metabolites from fluconazole-treated C. auris and fluconazole-treated C. auris–host cell co-culture demonstrated notable anti-Candida activity. Fluconazole caused significant reductions in C. auris cell numbers and aggregated phenotype. Metabolites produced by C. auris with potential fungal colonization, invasion, and host immune evasion effects were identified. Metabolites known to enhance biofilm formation produced during C. auris–host cell interaction were inhibited by fluconazole. Fluconazole enhanced the production of metabolites with biofilm inhibition activity, including behenyl alcohol and decanoic acid. Metabolites with potential Candida growth inhibition activity such as 2-palmitoyl glycerol, 1-tetradecanol, and 1-nonadecene were activated by fluconazole. Different patterns of proinflammatory cytokine expression presented due to fluconazole concentration and host cell type (fibroblasts versus macrophages). This highlights the immune response’s complexity, emphasizing the necessity for additional research to comprehend cell-type-specific responses to antifungal therapies. Both host cell interaction and fluconazole treatment increased the expression of CDR1 and ERG11 genes, both associated with drug resistance. This study provides insights into pathogenesis in C. auris due to host cell interaction and fluconazole treatment. Understanding these interactions is crucial for enhancing fluconazole sensitivity and effectively combating C. auris.

Orientia tsutsugamushi: An Unusual Intracellular Bacteria-Adaptation Strategies, Available Antibiotics, and Alternatives for Treatment.

During evolution Orientia tsutsugamushi became a smarter obligate bacterium to establish as intracellular pathogens. O. tsutsugamushi is a human pathogenic bacterium responsible for 1 billion infections of scrub typhus. Several novel mechanisms make this bacterium unique (cell wall, genetic constitutions, secretion system, etc.). In 2007, O. tsutsugamushi Boryong was pioneer strain for whole-genome sequencing. But the fundamental biology of this bacterial cell is a mystery till date. The unusual biology makes this organism as model for host cell interaction. Only a few antibiotics are effective against this intracellular pathogen but emergence of less susceptibility toward antibiotics make the situation alarming. The review was captivated to highlight the unusual aspects of adaptation, antibiotics, and drugs beyond antibiotics.

Clostridioides difficile Toxins: Host Cell Interactions and Their Role in Disease Pathogenesis.

Clostridioides difficile, a Gram-positive anaerobic bacterium, is the leading cause of hospital-acquired antibiotic-associated diarrhea worldwide. The severity of C. difficile infection (CDI) varies, ranging from mild diarrhea to life-threatening conditions such as pseudomembranous colitis and toxic megacolon. Central to the pathogenesis of the infection are toxins produced by C. difficile, with toxin A (TcdA) and toxin B (TcdB) as the main virulence factors. Additionally, some strains produce a third toxin known as C. difficile transferase (CDT). Toxins damage the colonic epithelium, initiating a cascade of cellular events that lead to inflammation, fluid secretion, and further tissue damage within the colon. Mechanistically, the toxins bind to cell surface receptors, internalize, and then inactivate GTPase proteins, disrupting the organization of the cytoskeleton and affecting various Rho-dependent cellular processes. This results in a loss of epithelial barrier functions and the induction of cell death. The third toxin, CDT, however, functions as a binary actin-ADP-ribosylating toxin, causing actin depolymerization and inducing the formation of microtubule-based protrusions. In this review, we summarize our current understanding of the interaction between C. difficile toxins and host cells, elucidating the functional consequences of their actions. Furthermore, we will outline how this knowledge forms the basis for developing innovative, toxin-based strategies for treating and preventing CDI.

A new hiPSC-based viral expression system to study virus host-cell interaction in hiPSC-derived cardiomyocytes

Abstract Coxsackievirus B3 (CVB3) belongs to the Picornaviridae family and is a member of the enterovirus genus. CVB3 is the most frequently detected pathogen in viral myocarditis, which leads to acute heart infections in 20-40% of cases and to dilated cardiomyopathy (DCM) in cases of prolonged viral persistence. Complex arrhythmias and sudden deaths due to CVB infections have also been reported, particularly in newborns and children. Observed arrhythmias include bradycardia, AV block and junctional ectopic tachycardia, suggesting that in addition to the functioning myocardium, the pacemaker cells and cardiac conduction system may also be impaired by CVB3 infection. The symptomatic phenotype is highly variable and depends on unclear host factors. It ranges from inconspicuous inflammation and rapid healing to acute congestive heart failure or viral persistence with progressive chronic disease. Despite the increasing and profound knowledge about viral myocarditis, it is still a challenge to identify further host factors that contribute to acute and chronic myocarditis, as science lacks sensitive and controllable disease models. The presented project shows the generation of a controlled, inducible virus-expressing hiPSC line that provides a solution for the beforementioned problems. The new human induced pluripotent stem cell line (hiPSC) i can be used to carry out virologic experiments in a controlled manner and without risk to the user. For this purpose, the modified and non-infectious genome of the enterovirus Coxsackievirus B3 (CVB3) is stably integrated into the genome of a wild-type hiPSC line. The CVB3 genome to be stably integrated was modified to prevent the formation of functional capsids by a DVP0 mutation. In addition, the 3'UTR and 5'UTR regions of the CVB3 genome were removed, which prevents uncontrolled self-replication of viral RNA. As a result, work with this CVB3DVP0-UTR genome is classified as S1 compliant. The expression of the CVB3DP0-UTR virus genome can be controlled by adding doxycycline to the cell culture medium by a TeT-On System. The transfected cells are then cultivated as clones and tested for virus expression. The dose-dependent CVB3DVP0 expression is verified using qPCR and FACS after 1 day of doxycycline application in the cell culture medium. Clones isolated and positively tested for CVB3 expression are used to carry out initial experiments on the interaction of the expressed viral proteins with the cell. Particular focus is placed on the induction of cell death, remodelling of the cytoskeleton and increase of reactive oxygen species (ROS) in mitochondria after CVB3DVP0-UTR induction in order to validate the cell system for application. Differentiation of the CVB3-expressing hiPSC-line into cardiomyocytes with subsequent virus induction results in the elevation of mitochondrial ROS, degradation of the cytoskeleton and arrhythmic behaviour of the cells.

Functional Divergence of the Paralog Salmonella Effector Proteins SopD and SopD2 and Their Contributions to Infection.

Salmonella enterica is a leading cause of bacterial food-borne illness in humans and is responsible for millions of cases annually. A critical strategy for the survival of this pathogen is the translocation of bacterial virulence factors termed effectors into host cells, which primarily function via protein-protein interactions with host proteins. The Salmonella genome encodes several paralogous effectors believed to have arisen from duplication events throughout the course of evolution. These paralogs can share structural similarities and enzymatic activities but have also demonstrated divergence in host cell targets or interaction partners and contributions to the intracellular lifecycle of Salmonella. The paralog effectors SopD and SopD2 share 63% amino acid sequence similarity and extensive structural homology yet have demonstrated divergence in secretion kinetics, intracellular localization, host targets, and roles in infection. SopD and SopD2 target host Rab GTPases, which represent critical regulators of intracellular trafficking that mediate diverse cellular functions. While SopD and SopD2 both manipulate Rab function, these paralogs display differences in Rab specificity, and the effectors have also evolved multiple mechanisms of action for GTPase manipulation. Here, we highlight this intriguing pair of paralog effectors in the context of host-pathogen interactions and discuss how this research has presented valuable insights into effector evolution.

Unveiling genome plasticity and a novel phage in Mycoplasma felis: Genomic investigations of four feline isolates.

Mycoplasma felis has been isolated from diseased cats and horses, but to date only a single fully assembled genome of this species, of an isolate from a horse, has been characterized. This study aimed to characterize and compare the completely assembled genomes of four clinical isolates of M. felis from three domestic cats, assembled with the aid of short- and long-read sequencing methods. The completed genomes encoded a median of 759 ORFs (range 743-777) and had a median average nucleotide identity of 98.2 % with the genome of the available equid origin reference strain. Comparative genomic analysis revealed the occurrence of multiple horizontal gene transfer events and significant genome reassortment. This had resulted in the acquisition or loss of numerous genes within the Australian felid isolate genomes, encoding putative proteins involved in DNA transfer, metabolism, DNA replication, host cell interaction and restriction modification systems. Additionally, a novel mycoplasma phage was detected in one Australian felid M. felis isolate by genomic analysis and visualized using cryo-transmission electron microscopy. This study has highlighted the complex genomic dynamics in different host environments. Furthermore, the sequences obtained in this work will enable the development of new diagnostic tools, and identification of future infection control and treatment options for the respiratory disease complex in cats.

Diverse animal models for Chlamydia infections: unraveling pathogenesis through the genital and gastrointestinal tracts.

Chlamydia trachomatis is responsible for infections in various mucosal tissues, including the eyes, urogenital, respiratory, and gastrointestinal tracts. Chronic infections can result in severe consequences such as blindness, ectopic pregnancy, and infertility. The underlying mechanisms leading to these diseases involve sustained inflammatory responses, yet thorough comprehension of the underlying mechanisms remains elusive. Chlamydial biologists employ in multiple methods, integrating biochemistry, cell biology, and genetic tools to identify bacterial factors crucial for host cell interactions. While numerous animal models exist to study chlamydial pathogenesis and assess vaccine efficacy, selecting appropriate models for biologically and clinically relevant insights remains a challenge. Genital infection models in animals have been pivotal in unraveling host-microbe dynamics, identifying potential chlamydial virulence factors influencing genital pathogenicity. However, the transferability of this knowledge to human pathogenic mechanisms remains uncertain. Many putative virulence factors lack assessment in optimal animal tissue microenvironments, despite the diverse chlamydial infection models available. Given the propensity of genital Chlamydia to spread to the gastrointestinal tract, investigations into the pathogenicity and immunological impact of gut Chlamydia become imperative. Notably, the gut emerges as a promising site for both chlamydial infection vaccination and pathogenesis. This review elucidates the pathogenesis of Chlamydia infections and delineates unique features of prevalent animal model systems. The primary focus of this review is to consolidate and summarize current animal models utilized in Chlamydia researches, presenting findings, discussions on their contributions, and suggesting potential directions for further studies.

Cryptococcus neoformans rapidly invades the murine brain by sequential breaching of airway and endothelial tissues barriers, followed by engulfment by microglia.

Cryptococcus neoformans causes lethal meningitis and accounts for approximately 10%-15% of AIDS-associated deaths worldwide. There are major gaps in our understanding of how this fungus invades the mammalian brain. To investigate the dynamics of C. neoformans tissue invasion, we mapped fungal localization and host cell interactions in infected brain, lung, and upper airways using mouse models of systemic and airway infection. To enable this, we developed an in situ imaging pipeline capable of measuring large volumes of tissue while preserving anatomical and cellular information by combining thick tissue sections, tissue clarification, and confocal imaging. We confirm high fungal burden in mouse upper airway after nasal inoculation. Yeast in turbinates were frequently titan cells, with faster kinetics than reported in mouse lungs. Importantly, we observed one instance of fungal cells enmeshed in lamina propria of the upper airways, suggesting penetration of airway mucosa as a possible route of tissue invasion and dissemination to the bloodstream. We extend previous literature positing bloodstream dissemination of C. neoformans, by finding viable fungi in the bloodstream of mice a few days after intranasal infection. As early as 24 h post systemic infection, the majority of C. neoformans cells traversed the blood-brain barrier, and were engulfed or in close proximity to microglia. Our work presents a new method for investigating microbial invasion, establishes that C. neoformans can breach multiple tissue barriers within the first days of infection, and demonstrates microglia as the first cells responding to C. neoformans invasion of the brain.IMPORTANCECryptococcal meningitis causes 10%-15% of AIDS-associated deaths globally. Still, brain-specific immunity to cryptococci is a conundrum. By employing innovative imaging, this study reveals what occurs during the first days of infection in brain and in airways. We found that titan cells predominate in upper airways and that cryptococci breach the upper airway mucosa, which implies that, at least in mice, the upper airways are a site for fungal dissemination. This would signify that mucosal immunity of the upper airway needs to be better understood. Importantly, we also show that microglia, the brain-resident macrophages, are the first responders to infection, and microglia clusters are formed surrounding cryptococci. This study opens the field to detailed molecular investigations on airway immune response, how fungus traverses the blood-brain barrier, how microglia respond to infection, and ultimately how microglia monitor the blood-brain barrier to preserve brain function.

Inhibition of PEDV viral entry upon blocking N-glycan elaboration

Porcine Epidemic Diarrhea Virus (PEDV) poses a significant threat to the global swine industry, demanding a thorough understanding of its cellular invasion mechanism for effective interventions. This study meticulously investigates the impact of O- and N-linked glycans on PEDV proteins and host cell interaction, shedding light on their influence on the virus's invasion process.Utilizing CRISPR-Cas9 technology to inhibit cell surface O- and N-linked glycan synthesis demonstrated no discernible impact on virus infection. However, progeny PEDV strains lacking these glycans exhibited a minor effect of O-linked glycans on virus infection. Conversely, a notable 40% reduction in infectivity was observed when the virus surface lacked N-linked glycans, emphasizing their pivotal role in facilitating virus recognition and binding to host cells.Additionally, inhibition studies utilizing kifunensine, a natural glycosidase I inhibitor, reaffirmed the significant role of N-linked glycans in virus infection. Inhibiting N-linked glycan synthesis with kifunensine substantially decreased virus entry into cells and potentially influenced spike protein expression.Assessment of the stability and recovery potential of N-linked glycan-deficient strains underscored the critical importance of N-glycans at various stages of the virus lifecycle. In vivo experiments infecting piglets with N-glycan-deficient strains exhibited milder clinical symptoms, reduced virus excretion, and less severe pathological lesions compared to conventional strains.These findings offer promising translational applications, proposing N-glycosylation inhibitors as potential therapeutic interventions against PEDV. The utilization of these inhibitors might mitigate virus invasion and disease transmission, providing avenues for effective antiviral strategies and vaccine development. Nonetheless, further research is warranted to elucidate the precise mechanisms of N-linked glycans in PEDV infection for comprehensive clinical applications.

Peptide selection via phage display to inhibit Leishmania-macrophage interactions.

Leishmaniasis comprises a complex group of diseases caused by protozoan parasites from the Leishmania genus, presenting a significant threat to human health. Infection starts by the release into the skin of metacyclic promastigote (MP) form of the parasite by an infected sand fly. Soon after their release, the MPs enter a phagocytic host cell. This study focuses on finding peptides that can inhibit MP-phagocytic host cell interaction. We used a phage display library to screen for peptides that bind to the surface of L. amazonensis (causative agent for cutaneous leishmaniasis) and L. infantum (causative agent for cutaneous and visceral leishmaniasis) MPs. Candidate peptide binding to the MP surface and inhibition of parasite-host cell interaction were tested in vitro. Peptide Inhibition of visceral leishmaniasis development was assessed in BALB/c mice. The selected L. amazonensis binding peptide (La1) and the L. infantum binding peptide (Li1) inhibited 44% of parasite internalization into THP-1 macrophage-like cells in vitro. While inhibition of internalization by La1 was specific to L. amazonensis, Li1 was effective in inhibiting internalization of both parasite species. Importantly, Li1 inhibited L. infantum spleen and liver infection of BALB/c mice by 84%. We identified one peptide that specifically inhibits L. amazonensis MP infection of host cells and another that inhibits both, L. amazonensis and L. infantum, MP infection. Our findings suggest a promising path for the development of new treatments and prevention of leishmaniasis.

Variation in the affinity of three representative avian adenoviruses for the cellular coxsackievirus and adenovirus receptor.

According to previous studies, three representative avian adenoviral strains utilize coxsackievirus-adenovirus receptor (CAR) as a receptor and seem to exhibit diverse binding affinities and modes. Thus, further revealing the exact molecular mechanism underlying the interaction between different FAdVs and the attachment receptor CAR is necessary. In this study, we successfully solved the crystal structure of the FAdV-4 fiber1 knob at 1.6 Å resolution. The interaction between the fibre knob and different domains of CAR was verified by confocal microscopy, coimmunoprecipitation and surface plasmon resonance (SPR) analysis. The fibre knobs of the three representative fowl adenoviruses specifically recognized CAR domain 1 (D1), but the recognition of CAR domain 2 (D2) by chicken embryo lethal orphan (CELO) strains was weak. These results provide insights into the differences in adenovirus‒host cell interactions and have important implications for the exploration of viral invasion mechanisms.

A Retrospective Analysis of Incidence and Risk Factors for the Development of Secondary Infections Following COVID-19

Abstract Introduction The SARS-CoV-2 virus primarily affects the lungs causing a heightened immune response due to viral and host cell interaction, which prompts the release of proinflammatory cytokines and reduces the defense mechanisms of the immune system, making the patient vulnerable to secondary infections. The study aims to identify the incidence and risk factors for secondary infections developing after COVID-19. Methods and Materials A retrospective study was conducted on 669 patients who were readmitted after COVID-19 to a tertiary care hospital. The development of secondary infections in these populations was identified. The data were collected from the medical records department. Statistical Analysis Incidence was calculated by the ratio of the total number of patients who developed secondary infections among readmitted patients divided by the total number of readmitted patients during the study period. Univariate analysis was performed to identify the statistically significant variables that were used in logistic regression for identifying the risk factors for secondary infection. Statistical analysis was performed in SPSS version 28.0. Results and Discussion In this study, 85 patients were found to have developed secondary infections with an incidence of 12.7%. Among the reported six infections, mucormycosis showed the highest incidence (34.1%), followed by sepsis and urinary tract infection. Nine patients developed tuberculosis as a post-COVID-19 secondary infection. General risk factors for secondary infections include male gender, presence of comorbidities such as diabetes mellitus and chronic kidney disease (CKD), intensive care unit (ICU) admission, elevated levels of interleukin-6 (IL-6) and D-dimer, and administration of steroids particularly medium-dose steroids. Conclusion Secondary infections can occur within 43 days of COVID-19 infection for every 12.7 per 100 patients in whom there is bacterial or fungal infections. Of these secondary infections, incidence of mucormycosis and sepsis was found to be higher in our study. COVID-19-infected patients who have either of these factors such as elevated inflammatory markers (Il-6 and D-dimer), the presence of comorbidities such as diabetes mellitus and CKD, ICU admission, and the use of steroids are at risk of developing secondary infections. Through proper screening, we can prevent patients who are at risk of developing secondary infections.

Intracellular symbiont Symbiodolus is vertically transmitted and widespread across insect orders.

Insects engage in manifold interactions with bacteria that can shift along the parasitism-mutualism continuum. However, only a small number of bacterial taxa managed to successfully colonize a wide diversity of insects, by evolving mechanisms for host-cell entry, immune evasion, germline tropism, reproductive manipulation, and/or by providing benefits to the host that stabilize the symbiotic association. Here, we report on the discovery of an Enterobacterales endosymbiont (Symbiodolus, type species Symbiodolus clandestinus) that is widespread across at least six insect orders and occurs at high prevalence within host populations. Fluorescence in situ hybridization in several Coleopteran and one Dipteran species revealed Symbiodolus' intracellular presence in all host life stages and across tissues, with a high abundance in female ovaries, indicating transovarial vertical transmission. Symbiont genome sequencing across 16 host taxa revealed a high degree of functional conservation in the eroding and transposon-rich genomes. All sequenced Symbiodolus genomes encode for multiple secretion systems, alongside effectors and toxin-antitoxin systems, which likely facilitate host-cell entry and interactions with the host. However, Symbiodolus-infected insects show no obvious signs of disease, and biosynthetic pathways for several amino acids and cofactors encoded by the bacterial genomes suggest that the symbionts may also be able to provide benefits to the hosts. A lack of host-symbiont cospeciation provides evidence for occasional horizontal transmission, so Symbiodolus' success is likely based on a mixed transmission mode. Our findings uncover a hitherto undescribed and widespread insect endosymbiont that may present valuable opportunities to unravel the molecular underpinnings of symbiosis establishment and maintenance.

Human alveolar lining fluid from the elderly promotes Mycobacterium tuberculosis intracellular growth and translocation into the cytosol of alveolar epithelial cells

The elderly population is highly susceptible to developing respiratory diseases, including tuberculosis (TB), a devastating disease caused by the airborne pathogen Mycobacterium tuberculosis (M.tb) that kills one person every 18 seconds. Once M.tb reaches the alveolar space, it contacts alveolar lining fluid (ALF), which dictates host cell interactions. We previously determined that age-associated dysfunction of soluble innate components in human ALF leads to accelerated M.tb growth within human alveolar macrophages. Here we determined the impact of human ALF on M.tb infection of alveolar epithelial cells (ATs), another critical lung cellular determinant of infection. We observed that elderly ALF (E-ALF)-exposed M.tb had significantly increased intracellular growth with rapid replication in ATs compared to adult ALF (A-ALF)-exposed bacteria, as well as a dampened inflammatory response. A potential mechanism underlying this accelerated growth in ATs was our observation of increased bacterial translocation into the cytosol, a compartment that favors bacterial replication. These findings in the context of our previous studies highlight how the oxidative and dysfunctional status of the elderly lung mucosa determines susceptibility to M.tb infection, including dampening immune responses and favoring bacterial replication within alveolar resident cell populations, including ATs, the most abundant resident cell type within the alveoli.

Working towards the development of vaccines and chemotherapeutics against neosporosis-With all of its ups and downs-Looking ahead.

Neospora caninum is an apicomplexan and obligatory intracellular parasite, which is the leading cause of reproductive failure in cattle and affects other farm and domestic animals, but also induces neuromuscular disease in dogs of all ages. In cattle, neosporosis is an important health problem, and has a considerable economic impact. To date there is no protective vaccine or chemotherapeutic treatment on the market. Immuno-prophylaxis has long been considered as the best control measure. Proteins involved in host cell interaction and invasion, as well as antigens mediating inflammatory responses have been the most frequently assessed vaccine targets. However, despite considerable efforts no effective vaccine has been introduced to the market to date. The development of effective compounds to limit the effects of vertical transmission of N. caninum tachyzoites has emerged as an alternative or addition to vaccination, provided suitable targets and safe and efficacious drugs can be identified. Additionally, the combination of both treatment strategies might be interesting to further increase protectivity against N. caninum infections and to decrease the duration of treatment and the risk of potential drug resistance. Well-established and standardized animal infection models are key factors for the evaluation of promising vaccine and compound candidates. The vast majority of experimental animal experiments concerning neosporosis have been performed in mice, although in recent years the numbers of experimental studies in cattle and sheep have increased. In this review, we discuss the recent findings concerning the progress in drug and vaccine development against N. caninum infections in mice and ruminants.

A Toxoplasma gondii thioredoxin with cell adhesion and antioxidant function.

Toxoplasma gondii (T. gondii) is a widespread, zoonotic protozoan intracellular parasite with a complex life cycle, which can cause toxoplasmosis, a potentially serious disease. During the invasion process, T. gondii proteins first bind to the relevant host cell receptors, such as glycosaminoglycan molecule (GAG-binding motif), which is one of the main receptors for parasites or virus to infect host cells. However, research on TGME49_216510 (T. gondii Trx21), a protein from Toxoplasma gondii, is limited. Bioinformatics analysis of the Trx21 protein was performed firstly. And specific primers were then designed using the conserved domain and GAG-binding motif to amplify, express, and purify a fragment of the Trx21 protein. The purified Trx21-GST protein was used for antioxidant and cell adhesion experiments. Simultaneously, mice were immunized with Trx21-His to generate specific polyclonal antibodies for subcellular localization analysis. The Trx21 protein, consisting of 774 amino acids, included a transmembrane region, three GAG-binding motifs, and a Thioredoxin-like domain. The recombinant Trx21-His protein had a molecular mass of about 31 kDa, while the Trx21-GST protein had a molecular mass of about 55 kDa, which was analyzed by SDS-PAGE and Western blot. Subcellular localization analysis by IFA revealed that Trx21 is predominantly distributed in the cytoplasm of T. gondii. Furthermore, Trx21 exhibited a protective effect on supercoiled DNA against metal-catalyzed oxidation (MCO) and demonstrated adhesion abilities to Vero cells. These results indicate that Trx21 plays an important role in host cell interaction and oxidative damage.

Bacterial Outer Membrane Vesicles: Role in Pathogenesis and Host-Cell Interactions.

Outer membrane vesicles (OMVs) are small, spherical structures released from the outer membranes of Gram-negative bacteria into the surrounding environment. Investigations into OMVs range from their biogenesis and cargo composition to their ability to transfer virulence factors and modulate host immune responses. This emerging understanding of OMVs has unveiled their pivotal role in the pathogenicity of infectious diseases, shedding light on their interactions with host cells, their contributions to inflammation, their potential involvement in antimicrobial resistance, and their promising use for the development of novel treatments and therapies. Numerous studies have associated the OMVs of pathogenic bacteria with the exacerbation of inflammatory diseases, underlining the significance of understanding the mechanisms associated with these vesicles to find alternatives for combating these conditions. Additionally, OMVs possess the ability to act as decoys, absorbing and neutralizing antibiotics, which significantly diminishes the efficacy of a broad spectrum of antimicrobial agents. Another subtopic of interest is OMVs produced by commensal microbiota. These vesicles are increasingly acknowledged for their mutualistic functions, significantly influencing their host's physiology and immune responses. Consequently, OMVs play a crucial role in maintaining a balanced gut microbiota by fostering symbiotic relationships that significantly contribute to the overall health and well-being of the host. This comprehensive review aims to provide an up-to-date review of OMVs derived from Gram-negative bacteria, summarizing current research findings, and elucidating the multifaceted role of these vesicles in diverse biological contexts.

Structure of the siphophage neck–Tail complex suggests that conserved tail tip proteins facilitate receptor binding and tail assembly

Siphophages have a long, flexible, and noncontractile tail that connects to the capsid through a neck. The phage tail is essential for host cell recognition and virus–host cell interactions; moreover, it serves as a channel for genome delivery during infection. However, the in situ high-resolution structure of the neck–tail complex of siphophages remains unknown. Here, we present the structure of the siphophage lambda “wild type,” the most widely used, laboratory-adapted fiberless mutant. The neck–tail complex comprises a channel formed by stacked 12-fold and hexameric rings and a 3-fold symmetrical tip. The interactions among DNA and a total of 246 tail protein molecules forming the tail and neck have been characterized. Structural comparisons of the tail tips, the most diversified region across the lambda and other long-tailed phages or tail-like machines, suggest that their tail tip contains conserved domains, which facilitate tail assembly, receptor binding, cell adsorption, and DNA retaining/releasing. These domains are distributed in different tail tip proteins in different phages or tail-like machines. The side tail fibers are not required for the phage particle to orient itself vertically to the surface of the host cell during attachment.

The Interactive Complex between Cytomegalovirus Kinase vCDK/pUL97 and Host Factors CDK7-Cyclin H Determines Individual Patterns of Transcription in Infected Cells.

The infection of human cytomegalovirus (HCMV) is strongly determined by the host-cell interaction in a way that the efficiency of HCMV lytic replication is dependent on the regulatory interplay between viral and cellular proteins. In particular, the activities of protein kinases, such as cyclin-dependent kinases (CDKs) and the viral CDK ortholog (vCDK/pUL97), play an important role in both viral reproduction and virus-host interaction. Very recently, we reported on the complexes formed between vCDK/pUL97, human cyclin H, and CDK7. Major hallmarks of this interplay are the interaction between cyclin H and vCDK/pUL97, which is consistently detectable across various conditions and host cell types of infection, the decrease or increase in pUL97 kinase activity resulting from cyclin H knock-down or elevated levels, respectively, and significant trans-stimulation of human CDK7 activity by pUL97 in vitro. Due to the fact that even a ternary complex of vCDK/pUL97-cyclin H-CDK7 can be detected by coimmunoprecipitation and visualized by bioinformatic structural modeling, we postulated a putative impact of the respective kinase activities on the patterns of transcription in HCMV-infected cells. Here, we undertook a first vCDK/pUL97-specific transcriptomic analysis, which combined conditions of fully lytic HCMV replication with those under specific vCDK/pUL97 or CDK7 drug-mediated inhibition or transient cyclin H knockout. The novel results were further strengthened using bioinformatic modeling of the involved multi-protein complexes. Our data underline the importance of these kinase activities for the C-terminal domain (CTD) phosphorylation-driven activation of host RNA polymerase in HCMV-infected cells. The impact of the individual experimental conditions on differentially expressed gene profiles is described in detail and discussed.