Colicin E9: Difference between revisions
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==Mechanism of uptake== | ==Mechanism 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. | 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<ref> PMID: 12804762 </ref>. The interaction with [[TolB]] is governed by a pentapeptide region in the N terminus. These residues are unstructured and highly flexible, but the TolB box of 5 residues is organised within this disordered domain<ref> PMID: 15452437 </ref>. | ||
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 | 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 | ||
<ref> PMID: 12804762 </ref>. | <ref> PMID: 12804762 </ref>. | ||
Once bound to the BtuB receptor, it is suggested that the coiled-coil receptor binding domain of the colicin unfolds to lose the immunity protein, Im9, and trigger translocation. This flexibility is crucial for translocation, and therefore the cytotoxicity, as shown by the addition of disulphide bonds. This reduces the flexibility and lowers the activity | Once bound to the BtuB receptor, it is suggested that the coiled-coil receptor binding domain of the colicin unfolds to lose the immunity protein, Im9, and trigger translocation. This flexibility is crucial for translocation, and therefore the cytotoxicity, as shown by the addition of disulphide bonds. This reduces the flexibility and lowers the activity<ref> PMID: 15231784 </ref>. | ||
The endonuclease domain of colicin E9 is able to form ion 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. The channels are then assumed to reseal themselves once the cytotoxic domain of the colicin has entered the cytoplasm. | The endonuclease domain of colicin E9 is able to form ion 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. The channels are then assumed to reseal themselves once the cytotoxic domain of the colicin has entered the cytoplasm. | ||