Colicin E9
Colicin E9 is a type of Colicin, a bacteriocin made by E. Coli which acts against other nearby E. Coli to kill them with its DNase activity; it digests the host's genome at specific locations, ultimately leading to the death of the cell.
Synthesis and releaseSynthesis and release
Mechanism of uptakeMechanism of uptake
The primary receptor for colicin E9 is the vitamin B12 receptor, BtuB. It then requires the outer membrane porin OmpF - either the two form the functional receptor, or OmpF is recruited for subsequent translocation. The OmpF association with the BtuB-colicin complex is weak and transient. After the interaction with OmpF, colicin E9 requires the Tol system to pass across the periplasm. OmpF acts synergistically with BtuB to protect bacteria against the action of colicin E9. This could indicate that OmpF is a component of the receptor apparatus. Alternatively the role of OmpF could be more to do with translocation rather than receptor recognition. [1]
The endonuclease activity of colicin E9 forms channels in planar lipid bilayers. The E9 DNase mediates its own translocation across the cytoplasmic membrane, and the formation of ion channels is essential to this process. The association of colicin E9 with negative phospholipids results in a destabilisation of the DNase. This is protected by the colE9 immunity protein, Im9, but not by the binding of zinc to the active site. Formation of this destabilising complex preempts channel formation by the DNase, and makes up the first step in the translocation of colE9 across the E. coli inner membrane.
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