Profiling of the assembly of RecA nucleofilaments implies a potential target for environmental factors to disturb DNA repair

Double-strand breaks (DSBs), one class of the most harmful DNA damage forms that bring elevated health risks, need to be repaired timely and effectively. However, an increasing number of environmental pollutants have been identified to impair DSB repair from various mechanisms. Our previous work indicated that the formation of unsaturated RecA nucleofilaments plays an essential role in homology recombination (HR) pathway which can accurately repair DSBs. In this study, by developing a benzonase cutting protection assay and combining it with traditional electrophoretic mobility shift assay (EMSA) analysis, we further investigated the assembly patterns of four RecA mutants that display differential DSB repair ability and ATPase activity. We observed that the mutants (G204S and S69G) possessing both ATP hydrolysis and DSB repair activities form unsaturated nucleofilaments similar to that formed by the wild type RecA, whereas the other two ATP hydrolysis-deficient mutants (K72R and E96D) that fail to mediate HR form more compacted nucleofilaments in the presence of ATP. These results establish a coupling of ATPase activity and effective DSB repair ability via the assembly status of RecA nucleofilaments. This linkage provides a potential target for environmental factors to disturb the essential HR pathway for DSB repair by suppressing the ATPase activity and altering the assembly pattern of nucleofilaments.     

Evaluation of 1,4-naphthoquinone derivatives as antibacterial agents: activity and mechanistic studies

● All 1,4-naphthoquinone hybrids exhibited significant antimicrobial activity. ● Presence of a hydroxyl group on aromatic B-ring of juglone was crucial for activity. ● Juglone can cause DNA damage by producing ROS and downregulation of RecA. ● Juglone has the potential to become a disinfectant. The diverse and large-scale application of disinfectants posed potential health risks and caused ecological damage during the 2019-nCoV pandemic, thereby increasing the demands for the development of disinfectants based on natural products, with low health risks and low aquatic toxicity. In the present study, a few natural naphthoquinones and their derivatives bearing the 1,4-naphthoquinone skeleton were synthesized, and their antibacterial activity against selected bacterial strains was evaluated. In vitro antibacterial activities of the compounds were investigated against Escherichia coli and Staphylococcus aureus. Under the minimum inhibitory concentration (MIC) of ≤ 0.125 μmol/L for juglone (1a), 5,8-dimethoxy-1,4-naphthoquinone (1f), and 7-methyl-5-acetoxy-1,4-naphthoquinone (3c), a strong antibacterial activity against S. aureus was observed. All 1,4-naphthoquinone derivatives exhibited a strong antibacterial activity, with MIC values ranging between 15.625 and 500 μmol/L and EC₅₀ values ranging between 10.56 and 248.42 μmol/L. Most of the synthesized compounds exhibited strong antibacterial activities against S. aureus. Among these compounds, juglone (1a) showed the strongest antibacterial activity. The results from mechanistic investigations indicated that juglone, a natural naphthoquinone, caused cell death by inducing reactive oxygen species production in bacterial cells, leading to DNA damage. In addition, juglone could reduce the self-repair ability of bacterial DNA by inhibiting RecA expression. In addition to having a potent antibacterial activity, juglone exhibited low cytotoxicity in cell-based investigations. In conclusion, juglone is a strong antibacterial agent with low toxicity, indicating that its application as a bactericidal agent may be associated with low health risks and aquatic toxicity.