Toxin-antitoxin (TA) systems are known to play various roles in physiological processes, such as gene regulation, growth arrest and survival, in bacteria exposed to environmental stress. Type II TA systems comprise natural complexes consisting of protein toxins and antitoxins. Each toxin and antitoxin participates in distinct regulatory mechanisms depending on the type of TA system. Recently, peptides designed by mimicking the interfaces between TA complexes showed its potential to activate the activity of toxin by competing its binding counterparts. Type II TA systems occur more often in pathogenic bacteria than in their nonpathogenic kin. Therefore, they can be possible drug targets, because of their high abundance in some pathogenic bacteria, such as Mycobacterium tuberculosis. In addition, recent bioinformatic analyses have shown that type III TA systems are highly abundant in the intestinal microbiota, and recent clinical studies have shown that the intestinal microbiota is linked to inflammatory diseases, obesity and even several types of cancer. We therefore focused on exploring the putative relationship between intestinal microbiota-related human diseases and type III TA systems. In this paper, we review and discuss the development of possible druggable materials based on the mechanism of type II and type III TA system.

Here, we report a simple hydrothermal method and in situ calcination to synthesize ZnO/K-CN x heterostructure nanocomposites. The optimized ZnO/K-CN0.5 exhibits excellent photocatalytic degradation and adsorption efficiency of tetracycline under simulated sunlight, and the degradation rate reaches 90% (the adsorption removal rate is 50%). Moreover, ZnO/K-CN0.5 also has high stability and recyclability. The excellent photocatalytic activity can be attributed to the following factors. (1) The K-doped exfoliated g-C3N4 nanosheet (K-CN) and the ZnO nanorod form a unique type-II heterojunction that promotes the separation of photogenerated carriers and provides very short photogenerated carrier diffusion distances. (2) The surface ζ-potential can enhance the adsorption capacity of tetracycline through electrostatic attraction and repulsion, resulting in synergistic effects of photocatalysis and adsorption. This work highlights the important role of integrating doping and exfoliation techniques into type-II heterojunctions to form nanocomposite photocatalyst materials, which have great potential in environmental water pollution treatment and the maintenance of human health.

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