The Mechanism Of Ag(?) And Hg(?) On The Assembly System Of E.coli Iron-sulfur Clusters

With the development of modern industry,heavy metal pollution has become an important factor threatening human safety.The use of soft metals as antibacterial materials has increasingly become the focus of toxicological mechanisms at home and abroad.Research on the toxicological mechanism of heavy metals has not reached a consistent conclusion.Because soft metals have strong sulfur affinity,the generation of toxicological mechanisms of softmetals may also have a close relationship with strong sulfur affinity.The sites they attack are likely to be those key sulfur-containing residues.The results of previous studies have shown that soft metals can directly destroy a type of key dehydratase exposed in E.coli cells [4Fe-4S].All levels occur simultaneously.In this study,E.coli was used as a model organism,and the soft metals Ag(I)and Hg(II)with the strongest sulfur affinity and toxicity were used as the objects to determine the sensitivity of E.coli to Ag(I)and Hg(II).The response of the E.coli Fe-S cluster assembly system under metal stress was analyzed,and the comprehensive oxidative stress regulator Oxy R,iron-sulfur cluster regulator Isc R,and iron were analyzed one by one through the construction of fusion strains,enzyme activity analysis,and transcriptome sequencing.The molecular mechanism of the regulator Fur's response to the activation of the Suf system.The results showed that the backup system Suf system of E.coli Fe-S cluster assembly was induced under Ag(I)stress,but the induced expression of Suf system under Hg(II)was not obvious.After knocking out the upstream Oxy R binding site,the Suf system is still induced and expressed,and the catalase regulated by Oxy R is not overexpressed;Isc R expression does not increase;Fur regulated downstream genes include sod A,fec A,fec B and other genes Be induced to express.Through the research,a mechanism of action of silver ion cytotoxicity is proposed: Ag(I)destroys the Fe/S cluster to assemble the Isc system and forces the cell to activate the backup system Suf.At the same time,the metal destroys the exposed [4Fe-4S] cluster in the Fe/S protein in the cell,resulting in the accumulation of a large number of apoenzymes.The cellular remodeling of Fe/S clusters increases the demand for Fe in the cells,making the cells deficient in Fe,and then regulates and initiates the expression of downstream genes in response to iron deficiency through Fur regulation.Fur directly induces the expression of suf operon and downstream genes through de-inhibition.This work reveals the important role played by sulfur affinity in metal toxicity,will provide a theoretical basis for clarifying the primary target of soft metal poisoning,and provide a new way to explain the toxicity of metals under oxygen-free conditions.