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Dear Readers, Welcome to the latest issue of The Magazine
Cytolethal distending toxins (CDTs) are a group of heterotrimeric toxins synthesized by specific gram-negative bacteria, which exhibit DNase activity. The aforementioned toxins induce G2/M cell cycle arrest in particular mammalian cell lines, resulting in the formation of larger or distended cells, which are commonly associated with these toxins. Cytolethal distending toxins are categorized as AB toxins, wherein the active (“A”) subunit exerts direct DNA damage, while the binding (“B”) subunit facilitates the attachment of the toxin to the target cells. The active component of CdtB has homology to mammalian DNase I, while the binding subunit is composed of CdtA and CdtC.
Gram-negative pathogenic bacteria belonging to the phylum Pseudomonadota are known to produce a class of toxins called cytolethal distending toxins. Several bacterial species, such as Shigella dysenteriae, Haemophilus ducreyi, and Escherichia coli, have the ability to cause infections in the human population.
The initial documented detection of a cytolethal-distending toxin occurred in 1987, within a pathogenic strain of Escherichia coli that was obtained from a juvenile patient.
The assembled toxin is characterized by its tripartite structure, comprising three different subunits known as CdtA, CdtB, and CdtC. In relation to its functionality, it can be classified as an AB toxin. Within this particular context, it is important to note that the CdtB subunit functions as the catalytically active “A” subunit, while the CdtA and CdtC subunits collectively constitute the binding “B” subunit. This binding subunit aids in the toxin’s ability to attach to and penetrate target cells. Certain scholarly literature utilizes the nomenclature AB2 to denote the structural composition of the toxin, which signifies the coexistence of both CdtA and CdtC components.
In contrast to other cytolethal distending toxins (CDTs), Salmonella enterica serovar Typhi CDT (SeCDT) lacks homologues of CdtA and CdtC. Nevertheless, it has been demonstrated that the Pertussis-like toxin A and B (pltA/pltB), which are encoded in close proximity to the active component cdtb, play a crucial role in cellular intoxication. The structures of PltA and PltB differ from those of CdtA and CdtC, hence inducing distinct mechanisms for enhancing CdtB activity.
The CDT toxin operates as an AB2 heterotrimeric toxin, wherein two regulatory subunits (CdtA and CdtC) are involved in facilitating the transportation of the active subunit (CdtB), which possesses the catalytic activity. The typhoid toxin generated by Salmonella enterica serovar Typhi similarly includes a CdtB subunit; however, it possesses a distinct A2B5 configuration. This configuration consists of a pentameric disc composed of five PltB regulatory subunits and two active subunits, namely CdtB and PltA. Notably, CdtB plays a crucial role in maintaining the pathogenic properties of the toxin. Upon initial examination, the analysis of the CdtB sequence did not exhibit any discernible similarities or homology to any proteins that are currently known or documented. During the early 2000s, the advent of novel software for protein sequence analysis facilitated the establishment of a correlation between CdtB and metalloenzymes exhibiting unique functional properties.
The B subunit of the CDT holotoxin, which is responsible for specifically targeting vulnerable cells with CdtB, consists of CdtA and CdtC. Both subunits exhibit low conservation, as the sequence identities across several taxa are frequently below 30%.
CDTs are organized in a singular operon and constitute a heterotrimeric toxin denoted as “AB2.” This toxin is composed of three subunits, namely CdtA, CdtB, and CdtC. The hypothesized mechanism is that CdtA and CdtC act in conjunction as the two binding components, referred to as “B” moieties, of the heterotrimeric AB2 toxin. These moieties facilitate the delivery of the active component, known as “A” moiety or CdtB, into the targeted cells. After attaching to the surface of the host cell, CDTs undergo internalization through clathrin-dependent endocytosis and are then transported from the cell surface through the Golgi apparatus and eventually reach the endoplasmic reticulum (ER).
The production of Cytolethal distending toxin (CDT) is attributed to many bacterial infections, wherein it manifests as a heterotrimeric protein toxin. When cells are exposed to CDT, they undergo cell death by either the activation of the mitotic checkpoint cascade or apoptosis. The identification of Cytolethal Distending Toxin (CDT) occurred in 1987 when a strain of Escherichia coli was obtained from a patient suffering from diarrhea. Subsequently, the manifestation of CDT has been documented in numerous pathogenic Gram-negative bacteria, such as Aggregatibacter (previously known as Actinobacillus) actinomycetemcomitans, Campylobacter spp., Escherichia albertii, Haemophilus ducreyi, Helicobacter spp., Providencia alcalifaciens, and Shigella spp.
The recombinant subunit A (cdtA) of the Cytolethal distending toxin from Escherichia coli is capable of reacting with E. coli. The purity of the sample was assessed using SDS-PAGE and found to be greater than 85%. The form or appearance of the substance is either in a liquid state or as a lyophilized powder, with a quantity of 100 micrograms.
Click here to know more: https://www.biorbyt.com/recombinant-escherichia-coli-c-orb1096009.html
