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

In silico simulation of glycosylation and related pathways

Glycans participate in a vast number of recognition systems in diverse organisms in health and in disease. However, glycans cannot be sequenced because there is no sequencer technology that can fully characterize them. There is no "template" for replicating glycans as there are for amino acids and nucleic acids. Instead, glycans are synthesized by a complicated orchestration of multitudes of glycosyltransferases and glycosidases. Thus glycans can vary greatly in structure, but they are not genetically reproducible and are usually isolated in minute amounts. To characterize (sequence) the glycome (defined as the glycans in a particular organism, tissue, cell, or protein), glycosylation pathway prediction using in silico methods based on glycogene expression data, and glycosylation simulations have been attempted. Since many of the mammalian glycogenes have been identified and cloned, it has become possible to predict the glycan biosynthesis pathway in these systems. By then incorporating systems biology and bioprocessing technologies to these pathway models, given the right enzymatic parameters including enzyme and substrate concentrations and kinetic reaction parameters, it is possible to predict the potentially synthesized glycans in the pathway. This review presents information on the data resources that are currently available to enable in silico simulations of glycosylation and related pathways. Then some of the software tools that have been developed in the past to simulate and analyze glycosylation pathways will be described, followed by a summary and vision for the future developments and research directions in this area.

Trauma-toxicology: concepts, causes, complications

Trauma and toxic substances are connected in several aspects. On the one hand, toxic substances can be the reason for traumatic injuries in the context of accidental or violent and criminal circumstances. Examples for the first scenario is the release of toxic gases, chemicals, and particles during house fires, and for the second scenario, the use of chemical or biological weapons in the context of terroristic activities. Toxic substances can cause or enhance severe, life-threatening trauma, as described in this review for various chemical warfare, by inducing a tissue trauma accompanied by break down of important barriers in the body, such as the blood-air or the blood-gut barriers. This in turn initiates a "vicious circle" as the contribution of inflammatory responses to the traumatic damage enhances the macro- and micro-barrier breakdown and often results in fatal outcome. The development of sophisticated methods for detection and identification of toxic substances as well as the special treatment of the intoxicated trauma patient is summarized in this review. Moreover, some highly toxic substances, such as the protein toxins from the pathogenic bacterium Clostridioides (C.) difficile, cause severe post-traumatic complications which significantly worsens the outcome of hospitalized patients, in particular in multiply injured trauma patients. Therefore, novel pharmacological options for the treatment of such patients are necessarily needed and one promising strategy might be the neutralization of the toxins that cause the disease. This review summarizes recent findings on the molecular and cellular mechanisms of toxic chemicals and bacterial toxins that contribute to barrier breakdown in the human body as wells pharmacological options for treatment, in particular in the context of intoxicated trauma patients. "trauma-toxicology" comprises concepts regrading basic research, development of novel pharmacological/therapeutic options and clinical aspects in the complex interplay and "vicious circle" of severe tissue trauma, barrier breakdown, pathogen and toxin exposure, tissue damage, and subsequent clinical complications.

Microscopy methods for Clostridioides difficile

Microscopic technologies including light and fluorescent, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and cryo-electron microscopy have been widely utilized to visualize Clostridioides difficile at the molecular, cellular, community, and structural biology level. This comprehensive review summarizes the microscopy tools (fluorescent and reporter system) in their use to study different aspects of C. difficile life cycle and virulence (sporulation, germination) or applications (detection of C. difficile or use of antimicrobials). With these developing techniques, microscopy tools will be able to find broader applications and address more challenging questions to study C. difficile and C. difficile infection.

An Updated View on the Cellular Uptake and Mode-of-Action of Clostridioides difficile Toxins

Research on the human gut pathogen Clostridioides (C.) difficile and its toxins continues to attract much attention as a consequence of the threat to human health posed by hypervirulent strains. Toxin A (TcdA) and Toxin B (TcdB) are the two major virulence determinants of C. difficile. Both are single-chain proteins with a similar multidomain architecture. Certain hypervirulent C. difficile strains also produce a third toxin, namely binary toxin CDT (C. difficile transferase). C. difficile toxins are the causative agents of C. difficile-associated diseases (CDADs), such as antibiotics-associated diarrhea and pseudomembranous colitis. For that reason, considerable efforts have been expended to unravel their molecular mode-of-action and the cellular mechanisms responsible for their uptake. Many of these studies have been conducted in European laboratories. Here, we provide an update on our previous review (Papatheodorou et al. Adv Exp Med Biol, 2018) on important advances in C. difficile toxins research.