The role of EvgS in the translocation pathway of colicin E7

• Main Authors: Jen-Chung Fan, 范仁忠
• Other Authors: Kin-Fu Chak
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/50864469571575997937

碩士 === 國立陽明大學 === 生物化學研究所 === 91 === Colicin E7 is a DNase type bacteriocin that released from E. coli during environmental stress and kills some closely related bacteria. So far, the mechanism of ColE7 translocation across the membrane of E. coli is still not very clear. In order to study the translocation process, a colicin resistant mutant library of E. coli has been created by Tn5 transposon mutagenesis. From the library, it was found that the manY mutant and the artP mutant are TolB and TolA deficient mutant, respectively, detected by Western blot analysis. These results suggested that TolA and TolB are essential for the translocation of DNase type colicin across the membrane of E. coli. Furthermore, the evgS mutant was found to be lacking ability to process the precursor form of TolB indicating that EvgS may be a possible regulator for the process of TolB in a Tol/Pal translocation pathway. It was found that the periplasmic extracts prepared from the wild type E. coli can process the DNase domain of colicin E7. However, the periplasmic extracts from the E. coli (tolB—) (the manY mutant) could not process the DNase domain of colicin. In contrast, the periplasmic extracts from the tolB complementary strain of the manY mutant, the ability of the process of DNase domain is recovered. This suggests that TolB may be involved in the process of ColE7 by generating toxicity domain in periplasm of E. coli. In this work, a possible mechanism for colicin E7 translocation is proposed. During the translocation process ColE7-Imm complex across the membrane of E. coli, the toxicity domain (DNase domain) in the C terminal of colicin may interact with TolB or probably with some other accessory proteins in the periplasmic space leading to the process of the DNase domain. Eventually, the processed DNase domain transverses the inner membrane to launch its cytotoxic effect in sensitive cells.