Colicin E9: Difference between revisions
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Colicin E9 is a type of [[Colicin]], an approximately 60kDa<ref> PMID: 15726170 </ref> bacteriocin made by ''E. | Colicin E9 is a type of [[Colicin]], an approximately 60kDa<ref> PMID: 15726170 </ref> 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 release== | ==Synthesis and release== | ||
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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<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>. | 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 (DGSGW) 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 | ||
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The cytotoxic activity of colE9 is DNase activity in the 15kDa C terminal domain, 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 cytotoxic activity of colE9 is DNase activity in the 15kDa C terminal domain, 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 | The DNase domain nicks dsDNA at thymine bases<ref> PMID: 15995205 </ref>. | ||
The catalytic centre of the DNase domain contains the H-N-H motif, a site for DNA and metal (zinc or nickel ion) binding. Binding zinc stabilises the protein<ref> PMID: 15044477 </ref>, and regulates the binding of phosphate ions to the active site. Upon binding to the metal ion, the conformation of the DNase alters. This diagram shows the binding of the metal ion and the phosphate to the DNase domain<ref> PMID: 15726170 </ref>. | |||
[[Image:From_15726170.png]] | [[Image:From_15726170.png]] | ||
In response to the DNA damage by colE9, the ''E. coli'' cell initiates an SOS response, prior to cell death<ref> PMID: 15044477 </ref>. | In response to the DNA damage by colE9, the ''E. coli'' cell initiates an SOS response, prior to cell death<ref> PMID: 15044477 </ref>. This involves the strong induction of 28 genes of the LexA-regulated SOS response<ref> PMID: 15995205 </ref>. | ||
==References== | ==References== | ||
<references/> | <references/> | ||