| Summary: | 博士 === 國立陽明大學 === 生化暨分子生物研究所 === 94 === The ColE7 operon contains ceaE7, ceiE7, and celE7 genes, which were regulated by an SOS responsive promoter. It is known that ColE7 was produced under stress conditions for killing competitive bacterium strains. During translocation (killing process) of ColE7 across the membrane of E. coli, the receptor-binding domain of ColE7 binds to the outer membrane BtuB receptor of susceptible cells. ColE7 further translocates into envelopes of the cells through its N-terminal translocation domain that interacts with membrane porins OmpF and OmpC as well as TolA/B/Q/R and Pal proteins. ColE7 is undergoing a modification process in the periplasmic space of the membrane, as a result the processed DNase domain will transverse the inner membrane into the cytoplasm for exerting cytotoxicity effect against its substrate chromosome DNA.
To trace any other factor located in the periplasmic space for the translocation of ColE7, periplasmic proteins isolated from E. coli cells treated with ColE7 were analyzed using proteomic approaches. In the experiments, we surprisingly found that the expression of two periplasmic proteins OppA and PotD was upregulated under ColE7 treatment. The production of OppA and PotD was tightly related to polyamine concentration and transportation, respectively. Accordingly, we attempt to study the relationships between ColE7 and polyamines in this paper.
Polyamines (putrescine and spermidine) were intermediary metabolites metabolized from ornithine, arginine, and lysine of the E. coli cells. Polyamines interact with acidic substances of the cell with their positive charged amino group under neutral pH. In this study, we found that polyamine syntheses were induced significantly when E. coli cells were under ColE7 exposure. We also found that polyamines render limited resistance to the cells against ColE7 toxicity. Meanwhile, polyamines were shown to be an essential factor for ColE7 production. Based on these observations, we propose that endogenous polyamines may participate in initiating the expression of the SOS response of the ColE7 operon and simultaneously down-regulate proteins that are responsible for colicin uptake, thus conferring a survival advantage on ColE7 producing E. coli under conditions of stress in the natural environment.
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