Protein Toxins Research Articles

Human α-Defensin-6 Neutralizes Clostridioides difficile Toxins TcdA and TcdB by Direct Binding.

Rising incidences and mortalities have drawn attention to Clostridioides difficile infections (CDIs) in recent years. The main virulence factors of this bacterium are the exotoxins TcdA and TcdB, which glucosylate Rho-GTPases and thereby inhibit Rho/actin-mediated processes in cells. This results in cell rounding, gut barrier disruption and characteristic clinical symptoms. So far, treatment of CDIs is limited and mainly restricted to some antibiotics, often leading to a vicious circle of antibiotic-induced disease recurrence. Here, we demonstrate the protective effect of the human antimicrobial peptide α-defensin-6 against TcdA, TcdB and the combination of both toxins in vitro and in vivo and unravel the underlying molecular mechanism. The defensin prevented toxin-mediated glucosylation of Rho-GTPases in cells and protected human cells, model epithelial barriers as well as zebrafish embryos from toxic effects. In vitro analyses revealed direct binding to TcdB in an SPR approach and the rapid formation of TcdB/α-defensin-6 complexes, as analyzed with fluorescent TcdB by time-lapse microscopy. In conclusion, the results imply that α-defensin-6 rapidly sequesters the toxin into complexes, which prevents its cytotoxic activity. These findings extend the understanding of how human peptides neutralize bacterial protein toxins and might be a starting point for the development of novel therapeutic options against CDIs.

Detection of Staphylococcal Enterotoxin A (SEA) using a sensitive nanomaterial-based electrochemical aptasensor

An electrochemical aptasensor was developed for SEA detection based on the application of chemically reduced graphene oxide and gold nano-urchins for enhancing sensitivity. The complex of the Staphylococcal Enterotoxin A (SEA) molecule and its specific aptamer on the nanomaterial-modified electrode is triggering the aptamer to be detached from the electrode surface and make a difference in the peak current of Differential pulse voltammetry. The fabrication process was confirmed using Cyclic Voltammetry, electrochemical impedance spectroscopy, and Scanning Electron Microscope imaging. As result, the limit of detection was 7.6 fM and the linear range was 25.0–950.0 fM of SEA. The selectivity assessment revealed the high specificity of the aptasensor towards SEA molecules compared to other similar toxin molecules and proteins. Moreover, the functionality of the developed system was tested successfully in spiked real samples of milk and meat as food samples and human serum as a clinical sample. These samples were also tested by a commercial ELISA kit of SEA to compare the results with the aptasensor. The test revealed that the recovery percentages and standard deviation of the aptasensor are superior to the ELISA kit. Therefore, the electrochemical aptasensor can be suggested for being used in food technologies and clinics to detect SEA toxin.

Invastigation of 16S rRNA, mecA and nuc genes in coagulase-positive and negative Staphylococci by Real-Time PCR

Staphylococcus aureus is a Gram-positive, round-shaped bacterium that is a member of the Firmicutes. It is often positive for catalase and nitrate reduction. Pathogenic strains often promote infections by producing virulence factors such as potent protein toxins, and the expression of a cell-surface protein that binds and inactivates antibodies. Sepsis-related to methicillin-resistant S. aureus (MRSA) has significant morbidity and high mortality rates (15-30%). The methicillin resistance for S. aureus is coded with the mecA gene, while the methicillin sensitivity is coded with the nuc gene, and they are chromosomal. Similarly, it is coded with the coagulase gene for S. aureus (Coa). In this study, the 16S rRNA gene identification by Real-Time PCR was investigated in forty S. aureus isolates, which were cultured at different times in terms of MIC and SIR tests. The isolates used in the study were determined at the gene level in terms of their differences in methicillin resistance gene (MecA), methicillin susceptibility gene (Nuc), coagulase gene (Coa) and in terms of intra-species differences were examined. As a result of the study, Staphylococcus spp. yielded positive results with 16S rRNA gene-specific primers in all isolates. Real-Time PCR analysis of the isolates with SYBRGreen-based PCR analysis was performed with 16S rRNA gene-specific primers, and the samples were confirmed to be Staphylococcus. Analysis at the family level was followed by Coa, Nuc, and MecA gene Real-Time PCR results, and it was found that, in terms of Coa and Nuc genes, 19 isolates were positive and 21 isolates were negative. In terms of MecA gene, 16 isolates were positive according to the positive sigmoidal curves and to the single peak melting values, whereas 24 isolates were found to be negative. It was thought that this study will benefit the community by contributing to the rapid and effective diagnosis and treatment of infections caused by coagulase positive and negative Staphylococci.

A comparison of two different analytical workflows to determine the venom proteome composition of Naja kaouthia from North-East India and immunological profiling of venom against commercial antivenoms

The Indian monocled cobra (Naja kaouthia) is one of the most prevalent venomous snakes in northeast India (NEI) and is the cause of many fatalities. The composition of NEI N. kaouthia venom (NkV) was deciphered using two different proteomic approaches: (i) 1D SDS-PAGE coupled to label-free quantification of protein bands using stringent identification criteria and (ii) reversed-phase high-performance liquid chromatography (RP-HPLC) followed by quantification based on area under the RP-HPLC peaks. The proteomic data from both strategies were compared. Proteomic analyses from both workflows identified 32 proteins (toxins) distributed over 10–14 snake venom protein families in NEI NkV. The relative abundances of the venom proteins determined from the analytical workflows coincided with the densitometry band intensities of the NEI NkV. Phospholipase A2 (13.1–16.0%) and three-finger toxins (58.5–64.2%) represented the most abundant enzymatic and non-enzymatic proteins in NEI NkV, respectively. Immuno-cross-reactivity studies by enzyme-linked immunoassay and immunoblot analyses pointed to the poor efficacy of commercial PAVs in recognizing the low molecular mass (<15 kDa) toxins of NEI NkV. Spectrofluorometric titration determined the presence of NEI NkV-specific antibodies in commercial PAV, at a level that was higher than that previously reported for eastern India NkV-specific antibodies in commercial antivenom.

Luteolin attenuates the pathogenesis of Staphylococcus aureus by interfering with the agr system

Staphylococcus aureus is a serious human pathogen that causes a wide variety of infectious diseases with high morbidity and mortality. Luteolin was recently shown to inhibit biofilm formation and reduce the production of virulence factors and the transcription of agrA in S. aureus. Given the broad impacts of the agr quorum-sensing system on the biofilm formation and virulence factors of S. aureus, this study aimed to investigate the effects of luteolin on the agr system and pathogenicity of S. aureus. Here, we show that at subminimal inhibitory concentrations (sub-MICs) that have no effect on bacterial growth, luteolin can markedly inhibit the adhesion and biofilm formation of both wild-type (WT) and agr mutant strains of S. aureus strain Newman. The hemolytic activity and toxin protein levels were markedly decreased in the culture supernatants of luteolin-treated WT strain but not the luteolin-treated agr mutant strain. qRT–PCR analysis showed that upon luteolin treatment, the expression of genes involved in virulence and biofilm formation was downregulated in the WT S. aureus strain, and the inefficacy of luteolin with respect to the virulence factors of only the agr mutant confirmed the agr-mediated antivirulence potential of luteolin. Furthermore, treatment with sub-MIC luteolin attenuated human alveolar epithelial A549 cell injury caused by the WT Newman strain and protected mice from pneumonia caused by the WT strain, but these effects were not observed with the agr mutant strain. These findings indicate that luteolin is a promising compound that interferes with the agr system and can be developed into novel therapeutic drugs against S. aureus infections.

Membrane Dynamics and Remodelling in Response to the Action of the Membrane-Damaging Pore-Forming Toxins.

Pore-forming protein toxins (PFTs) represent a diverse class of membrane-damaging proteins that are produced by a wide variety of organisms. PFT-mediated membrane perforation is largely governed by the chemical composition and the physical properties of the plasma membranes. The interaction between the PFTs with the target membranes is critical for the initiation of the pore-formation process, and can lead to discrete membrane reorganization events that further aids in the process of pore-formation. Punching holes on the plasma membranes by the PFTs interferes with the cellular homeostasis by disrupting the ion-balance inside the cells that in turn can turn on multiple signalling cascades required to restore membrane integrity and cellular homeostasis. In this review, we discuss the physicochemical attributes of the plasma membranes associated with the pore-formation processes by the PFTs, and the subsequent membrane remodelling events that may start off the membrane-repair mechanisms.

Electrochemical impedance spectrum reveals structural details of distribution of pores and defects in supported phospholipid bilayers

In this study we developed a methodology for solving an inverse problem to obtain structural information about distribution of nanoscale defects in surface supported, tethered bilayer membranes (tBLMs) using the electrochemical impedance spectroscopy (EIS) technique. We demonstrate that the EIS spectra contain physical information about the electrical and structural parameters of tBLMs as well as information about distribution of density of defects in membranes. Such defects can be naturally occurring collapsed sites of bilayers due to imperfections of solid substrates onto which tBLMs are assembled. Also, the membrane defects can be introduced artificially by insertion of pore-forming toxin proteins into phospholipid bilayers or by other means such as electroporation. The proposed methodology can be used for the development of precision biosensors sensitive to agents impairing integrity of biological membranes, and in general studies of protein membrane interactions that involves damage of phospholipid bilayers.

Combined proteomic strategies for in-depth venomic analysis of the beaked sea snake (Hydrophis schistosus) from Songkhla Lake, Thailand

This study focuses on comprehensive characterization of the venom proteome of the beaked sea snake (Hydrophis schistosus) from Songkhla Lake, Thailand. H. schistosus can be considered as the deadliest sea snake commonly found in the Pacific and Indian oceans. Their envenomation causes muscular paralysis and rhabdomyolysis. To develop effective treatment for this snakebite, it is necessary to understand the detailed venom composition. In this study, multiple mass spectrometry-based approaches were employed. Bottom-up proteomics revealed that tryptic digestion in-solution provided a higher number of toxin proteins identified and a larger sequence coverage, compared to in-gel digestion. In addition, a venom gland transcriptome-derived database was constructed and used as a reference, which 43 known and novel toxin proteins were identified using this database and the UniProtKB. Three-finger toxin and phospholipase A2 were shown to be top two most abundant protein families. Minor compositions included other toxin families and a number of non-toxin proteins. Moreover, a hybrid de novo sequencing was performed to enhance identification of the small proteins/peptides. Using non-digested samples, there were 46 predicted toxin peptides. The finding from this study could lead to a better understanding in pathological effects of the snakebite and the future development of effective antivenoms. SignificanceThis study provides a better understanding of the venom proteome composition of the beaked sea snake (H. schistosus) found in the Gulf of Thailand, using a combination of different sample preparation techniques, Serpentes protein database searching, transcriptome-derived protein database searching, and a hybrid de novo peptide sequencing strategy. It revealed 13 toxin protein families and novel proteins in the beaked sea snake venom including new species of phospholipase A2s (PLA2s) and three-finger toxins (3FTxs). It could serve as a basis for the development of snakebite treatments and for the discovery of novel pharmaceutical drugs from the toxin peptides.

Peptide Toxins as Biothreats and the Potential for AI Systems to Enhance Biosecurity.

Biological weapons have been used for thousands of years, but recent advances in synthesis technologies have made peptide and protein toxin production more accessible and pose a threat to biosecurity worldwide. Natural toxins such as conotoxins, certain hemolytic compounds, and enterotoxins are peptide agents that can be synthesized in an environment with weak biosecurity measures and rudimentarily weaponized for limited use against smaller targets for lethal or nonlethal effects. Technological advances are changing the threat landscape around biological weapons and potentially facilitating a shift from state sponsored to more micro-level threats stemming from terror cells, insider threats, and lone wolf attacks. Here, we present the reader with an overview of the threat of peptide and protein toxins, provide examples of potent peptide toxins, and introduce capabilities of a proposed biosecurity program utilizing artificial intelligence that unifies commercial nucleotide and peptide synthesis vendors.

The Essential Role of Rac1 Glucosylation in Clostridioides difficile Toxin B-Induced Arrest of G1-S Transition.

Clostridioides difficile infection (CDI) in humans causes pseudomembranous colitis (PMC), which is a severe pathology characterized by a loss of epithelial barrier function and massive colonic inflammation. PMC has been attributed to the action of two large protein toxins, Toxin A (TcdA) and Toxin B (TcdB). TcdA and TcdB mono-O-glucosylate and thereby inactivate a broad spectrum of Rho GTPases and (in the case of TcdA) also some Ras GTPases. Rho/Ras GTPases promote G1-S transition through the activation of components of the ERK, AKT, and WNT signaling pathways. With regard to CDI pathology, TcdB is regarded of being capable of inhibiting colonic stem cell proliferation and colonic regeneration, which is likely causative for PMC. In particular, it is still unclear, the glucosylation of which substrate Rho-GTPase is critical for TcdB-induced arrest of G1-S transition. Exploiting SV40-immortalized mouse embryonic fibroblasts (MEFs) with deleted Rho subtype GTPases, evidence is provided that Rac1 (not Cdc42) positively regulates Cyclin D1, an essential factor of G1-S transition. TcdB-catalyzed Rac1 glucosylation results in Cyclin D1 suppression and arrested G1-S transition in MEFs and in human colonic epithelial cells (HCEC), Remarkably, Rac1−/− MEFs are insensitive to TcdB-induced arrest of G1-S transition, suggesting that TcdB arrests G1-S transition in a Rac1 glucosylation-dependent manner. Human intestinal organoids (HIOs) specifically expressed Cyclin D1 (neither Cyclin D2 nor Cyclin D3), which expression was suppressed upon TcdB treatment. In sum, Cyclin D1 expression in colonic cells seems to be regulated by Rho GTPases (most likely Rac1) and in turn seems to be susceptible to TcdB-induced suppression. With regard to PMC, toxin-catalyzed Rac1 glucosylation and subsequent G1-S arrest of colonic stem cells seems to be causative for decreased repair capacity of the colonic epithelium and delayed epithelial renewal.

Novel Strategies to Inhibit Pertussis Toxin.

Pertussis, also known as whooping cough, is a respiratory disease caused by infection with Bordetella pertussis, which releases several virulence factors, including the AB-type pertussis toxin (PT). The characteristic symptom is severe, long-lasting paroxysmal coughing. Especially in newborns and infants, pertussis symptoms, such as leukocytosis, can become life-threatening. Despite an available vaccination, increasing case numbers have been reported worldwide, including Western countries such as Germany and the USA. Antibiotic treatment is available and important to prevent further transmission. However, antibiotics only reduce symptoms if administered in early stages, which rarely occurs due to a late diagnosis. Thus, no causative treatments against symptoms of whooping cough are currently available. The AB-type protein toxin PT is a main virulence factor and consists of a binding subunit that facilitates transport of an enzyme subunit into the cytosol of target cells. There, the enzyme subunit ADP-ribosylates inhibitory α-subunits of G-protein coupled receptors resulting in disturbed cAMP signaling. As an important virulence factor associated with severe symptoms, such as leukocytosis, and poor outcomes, PT represents an attractive drug target to develop novel therapeutic strategies. In this review, chaperone inhibitors, human peptides, small molecule inhibitors, and humanized antibodies are discussed as novel strategies to inhibit PT.

Bacterial pore-forming toxins.

Pore-forming toxins (PFTs) are widely distributed in both Gram-negative and Gram-positive bacteria. PFTs can act as virulence factors that bacteria utilise in dissemination and host colonisation or, alternatively, they can be employed to compete with rival microbes in polymicrobial niches. PFTs transition from a soluble form to become membrane-embedded by undergoing large conformational changes. Once inserted, they perforate the membrane, causing uncontrolled efflux of ions and/or nutrients and dissipating the protonmotive force (PMF). In some instances, target cells intoxicated by PFTs display additional effects as part of the cellular response to pore formation. Significant progress has been made in the mechanistic description of pore formation for the different PFTs families, but in several cases a complete understanding of pore structure remains lacking. PFTs have evolved recognition mechanisms to bind specific receptors that define their host tropism, although this can be remarkably diverse even within the same family. Here we summarise the salient features of PFTs and highlight where additional research is necessary to fully understand the mechanism of pore formation by members of this diverse group of protein toxins.

“From Protein Toxins to Applied Toxicological Testing” virtual workshop identifies the need for a bioinformatic framework to assess novel food protein safety

On October 21–22, 2020 the HESI (Health and Environmental Sciences Institute) Protein Allergens, Toxins, and Bioinformatics Committee, and the Society of Toxicology Food Safety Specialty Section co-hosted a virtual workshop titled “From Protein Toxins to Applied Toxicological Testing”. The workshop focused on the safety assessment of novel proteins contained in foods and feeds, was globally represented by over 200 stakeholder attendees, and featured contributions from experts in academia, government and non-government organizations, and agricultural biotechnology developers from the private sector. A range of topics relevant to novel protein safety were discussed, including: the state of protein toxin biology, modes and mechanisms of action, structures and activity, use of bioinformatic analyses to assess the safety of a protein, and ways to leverage computational biology with in silico approaches for protein toxin identification/characterization. Key outcomes of the workshop included the appreciation of the complexity of developing a definition for a protein toxin when viewed from the perspective of food and feed safety, confirming the need for a case-by-case hypothesis-driven interpretation of bioinformatic results that leverages additional metadata rather than an alignment threshold-driven interpretation, and agreement that a “toxin protein database” is not necessary, as the bioinformatic needs for toxin detection may be accomplished by existing databases such as Pfam and UniProtKB/Swiss-Prot. In this paper, a path forward is proposed.

Effect of N-vinylimidazole comonomer on blood plasma protein and endogenous toxin adsorption on mesoporous copolymer beads

N-vinylimidazole-divinylbenzene (VI-DVB) copolymer beads with a N-vinylimidazole (VI) weight content ranging from 7% to 15% were studied as possible adsorbents for hemoperfusion and compared with the cross-linked polystyrene beads from commercial devices. All the beads had a large volume fraction of mesopores with diameters of 2–50 nm, quantified by nitrogen adsorption, and BET areas from 500 to 1000 m²/g. Metal-chelate adsorption of copper (II) ions on VI-DVB was high in 0.15 M NaCl (up to 40 μmol/mL), and low in blood plasma (< 1 μmol/mL). Reversible adsorption of blood plasma proteins was high (> 100 mg/mL beads) on all the bead types. Irreversibly adsorbed proteins eluted by 2% SDS included albumin, fibrinogen, fibronectin, and transferrin. Metal chelating contributed to the irreversible adsorption. Unlike the beads from commercial devices, VI-DVB beads adsorbed the LPS endotoxin from plasma. Adsorption of bilirubin and IL-6 was high on all the beads tested, but VI-DVB beads were better adsorbents of bile acids. VI-DVB are promising as components of multifunctional devices for blood purification applicable to treatment of diseases where conventional devices have lower or negligible adsorption capacity.

The medusa of Aurelia coerulea is similar to its polyp in molecular composition and different from the medusa of Stomolophus meleagris in toxicity

BackgroundThe incidents of Aurelia sp. stinging have recently increased because of a bloom in offshore area. However, their symptoms are much milder than those from another scyphozoan jellyfish, Stomolophus meleagris. MethodsThe molecular composition of the medusa and polyp of Aurelia coerulea was analyzed by sequencing the transcriptome and proteome. The toxicity of tentacle extract from A. coerulea medusa (A-TE) and S. meleagris medusa (S-TE) was measured by the survival rates of mice, their blood indexes, and integrity of red blood cells. ResultsThe medusa and polyp of A. coerulea are similar in molecular composition, while their gene expressions are significantly different at both transcriptome and proteome levels. A-TE displayed no in vitro hemolysis and caused mild damage to the liver, heart and kidney instead of lethality. In contrast, S-TE showed strong hemolytic toxicity, and lethal effect with serious damage to the liver, heart and kidney. The toxin screening in the medusae showed that there were similar toxin categories though the number of toxin species in A. coerulea was larger than that in S. meleagris. Among them, lactotransferrin and venom prothrombin activator were the two predominant protein toxins in the medusae of A. coerulea and S. meleagris, respectively. ConclusionsA. coerulea medusa and polyp have similar molecular compositions, though there are observable morphological differences. The toxicity of A. coerulea medusa is significantly weaker than that of S. meleagris medusa of which the variation in toxin expressions is feasibly an important reason.

Glucosyltransferase-dependent and independent effects of Clostridioides difficile toxins during infection.

Clostridioides difficile infection (CDI) is the leading cause of nosocomial diarrhea and pseudomembranous colitis in the USA. In addition to these symptoms, patients with CDI can develop severe inflammation and tissue damage, resulting in life-threatening toxic megacolon. CDI is mediated by two large homologous protein toxins, TcdA and TcdB, that bind and hijack receptors to enter host cells where they use glucosyltransferase (GT) enzymes to inactivate Rho family GTPases. GT-dependent intoxication elicits cytopathic changes, cytokine production, and apoptosis. At higher concentrations TcdB induces GT-independent necrosis in cells and tissue by stimulating production of reactive oxygen species via recruitment of the NADPH oxidase complex. Although GT-independent necrosis has been observed in vitro, the relevance of this mechanism during CDI has remained an outstanding question in the field. In this study we generated novel C. difficile toxin mutants in the hypervirulent BI/NAP1/PCR-ribotype 027 R20291 strain to test the hypothesis that GT-independent epithelial damage occurs during CDI. Using the mouse model of CDI, we observed that epithelial damage occurs through a GT-independent process that does not involve immune cell influx. The GT-activity of either toxin was sufficient to cause severe edema and inflammation, yet GT activity of both toxins was necessary to produce severe watery diarrhea. These results demonstrate that both TcdA and TcdB contribute to disease pathogenesis when present. Further, while inactivating GT activity of C. difficile toxins may suppress diarrhea and deleterious GT-dependent immune responses, the potential of severe GT-independent epithelial damage merits consideration when developing toxin-based therapeutics against CDI.

Risk compounds, potential mechanisms and biomarkers of traditional Chinese medicine-induced reproductive toxicity.

With the increasing application of traditional Chinese medicine (TCM), TCM-induced reproductive toxicity has gradually aroused people's concern. Various TCM, such as Tripterygium wilfordii Hook. f., Radix Aconiti lateralis Preparata and Rhizoma Pinelliae, are currently reported to cause reproductive toxicity in humans and animals. However, a summary of the material bases, mechanisms and biological markers of TCM-induced reproductive toxicity is still lacking. This review filled the gap by searching and summarising relevant studies and articles published on PubMed, CNKI and Web of Science databases from January 2000 to November 2021. The risk ingredients involved in TCM-induced reproductive toxicity were divided into glycosides, alkaloids, phenols, terpenoids, anthraquinones, lactones, plant toxin proteins, animal toxins and so forth. Potential mechanisms underlying TCM-induced reproductive toxicity, including steroidogenic toxicity, lipids metabolism abnormity, energy insufficiency, oxidative stress and apoptosis, were illustrated. We also outlined possible biomarkers, especially biomarkers of effect involved in TCM-induced reproductive toxicity, including anti-oxidant enzymes, signalling pathways, genes and growth factors.

Molecularly engineered tumor acidity-responsive plant toxin gelonin for safe and efficient cancer therapy.

Due to the unsatisfactory therapeutic efficacy and inexorable side effects of small molecule antineoplastic agents, extensive efforts have been devoted to the development of more potent macromolecular agents with high specificity. Gelonin is a plant-derived protein toxin that exhibits robust antitumor effect via inactivating ribosomes and inhibiting protein synthesis. Nonetheless, its poor internalization ability to tumor cells has compromised the therapeutic promise of gelonin. In this study, a tumor acidity-responsive intracellular protein delivery system ─ functional gelonin (Trx-pHLIP-Gelonin, TpG) composed of a thioredoxin (Trx) tag, a pH low insertion peptide (pHLIP) and gelonin, was designed and obtained by genetic recombination technique for the first time. TpG could effectively enter into tumor cells under weakly acidic conditions and markedly suppress tumor cell proliferation via triggering cell apoptosis and inhibiting protein synthesis. Most importantly, treatment by intravenous injection into subcutaneous SKOV3 solid tumors in a mouse model showed that TpG was much more effective than gelonin in curtailing tumor growth rates with negligible toxicity. Collectively, our present work suggests that the tumor acidity-targeted delivery manner endowed by pHLIP offers a new avenue for efficient delivery of other bioactive substances to acidic diseased tissues.

Role of PemI in the Staphylococcus aureus PemIK toxin-antitoxin complex: PemI controls PemK by acting as a PemK loop mimic.

Staphylococcus aureus is a notorious and globally distributed pathogenic bacterium. New strategies to develop novel antibiotics based on intrinsic bacterial toxin–antitoxin (TA) systems have been recently reported. Because TA systems are present only in bacteria and not in humans, these distinctive systems are attractive targets for developing antibiotics with new modes of action. S. aureus PemIK is a type II TA system, comprising the toxin protein PemK and the labile antitoxin protein PemI. Here, we determined the crystal structures of both PemK and the PemIK complex, in which PemK is neutralized by PemI. Our biochemical approaches, including fluorescence quenching and polarization assays, identified Glu20, Arg25, Thr48, Thr49, and Arg84 of PemK as being important for RNase function. Our study indicates that the active site and RNA-binding residues of PemK are covered by PemI, leading to unique conformational changes in PemK accompanied by repositioning of the loop between β1 and β2. These changes can interfere with RNA binding by PemK. Overall, PemK adopts particular open and closed forms for precise neutralization by PemI. This structural and functional information on PemIK will contribute to the discovery and development of novel antibiotics in the form of peptides or small molecules inhibiting direct binding between PemI and PemK.

T-DNA integration and its effect on gene expression in dual Bt gene transgenic Populus ×euramericana cv. Neva

The integration of Bacillus thuringiensis (Bt) genes is often accompanied by unintended effects along with the improved resistance to targeted pests. The insertion information of transfer DNA (T-DNA) and the expression information of upstream and downstream genes are of great significance for related research on unexpected effects and molecular-level mechanisms. In this study, six dual Bt transgenic Populus × euramericana cv. Neva (poplar 107) lines were used as research objects. We determined growth and physiological indices, and characterized the T-DNA integration using next-generation sequencing technology. The transgenic and non-transgenic lines showed no significant difference in growth index. However, while insect resistance was enhanced, effects related to the integration sites of the Bt gene occurred. A total of 15 insertion sites were detected among the six transgenic lines, and T-DNA preferentially inserted into AT-rich regions of the poplar genome. RNA sequencing and weighted gene co-expression network analysis were used to explore the effects of T-DNA insertion on the gene expression of poplar 107. As a result, the metabolic pathways most affected by the Bt gene were starch and sucrose metabolism and pentose and gluconate conversion. The expression of exogenous Bt had a greater impact than the insertion position or copy number on poplar 107 gene expression, and the Cry1Ac toxin protein also played a major role. This study provides theoretical support for the cultivation and management of poplar 107 new varieties, and provides reference for Poplar insect resistance breeding and its molecular response to Bt gene.