Colicin E9: Difference between revisions
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==Synthesis and release== | ==Synthesis and release== | ||
Colicin E9 in solution, ie in the cytoplasm after synthesis, is monomeric, and forms a high affinity complex with its immunity protein, Im9. The immunity protein does not directly bind to the active site, but instead to an exosite. <ref> PMID: 15044477 </ref> | Colicin E9 in solution, ie in the cytoplasm after synthesis, is monomeric, and forms a high affinity complex with its immunity protein, Im9. The immunity protein does not directly bind to the active site, but instead to an exosite. This is bound while in the producing cell to protect it from the activity<ref> PMID: 15044477 </ref>. | ||
==Mechanism of uptake== | ==Mechanism of uptake== | ||
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The destabilisation of the DNase domain upon interaction with negative phospholipids increases its susceptibility to proteolysis and to thermal and chemical denaturation. Once associated, there is a massive disruption of protein tertiary structure, and the secondary structure instead interacts with the lipid bilayer - similar to the interaction between domains involved in [[Pore Formation]] in other colicins and the membranes that they disrupt. | The destabilisation of the DNase domain upon interaction with negative phospholipids increases its susceptibility to proteolysis and to thermal and chemical denaturation. Once associated, there is a massive disruption of protein tertiary structure, and the secondary structure instead interacts with the lipid bilayer - similar to the interaction between domains involved in [[Pore Formation]] in other colicins and the membranes that they disrupt. | ||
The formation of a disulphide bond at D20C/E66C abolishes its channel forming ability, and its cytotoxicity (as it cannot penetrate cells) but has no effect on its DNase activity. It is still able to bind to the phospholipids, but not translocate across the membrane | The formation of a disulphide bond at D20C/E66C abolishes its channel forming ability, and its cytotoxicity (as it cannot penetrate cells) but has no effect on its DNase activity. It is still able to bind to the phospholipids, but not translocate across the membrane<ref> PMID: 15044477 </ref>. | ||
==Killing Activities== | ==Killing Activities== | ||
The cytotoxic activity of colE9 is DNase activity, where it hydrolyses the DNA | The cytotoxic activity of colE9 is DNase activity, where it hydrolyses the DNA<ref> PMID: 12804762 </ref> <ref> PMID: 15452437 </ref>. However, it is also able to form ion channels in planar lipid bilayers, similar to the pore-forming colicins. These channels do not cause cell death, instead they are related to the ability of the E9 DNase domain to translocate across the inner membrane. | ||
The catalytic centre of the DNase domain contains the HNH motif, a site for DNA and metal (zinc ion) binding. Binding zinc stabilises the protein. | The catalytic centre of the DNase domain contains the HNH motif, a site for DNA and metal (zinc ion) binding. Binding zinc stabilises the protein. | ||
In response to the DNA damage by colE9, the ''E. coli'' cell initiates an SOS response, prior to cell death | In response to the DNA damage by colE9, the ''E. coli'' cell initiates an SOS response, prior to cell death<ref> PMID: 15044477 </ref>. | ||
==References== | ==References== | ||
<references/> | <references/> | ||