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> 15044477 </ref> | |||
==Mechanism of uptake== | ==Mechanism of uptake== | ||
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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. | 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. | ||
To aid the colicin in crossing the inner membrane, the colicin has the ability to form ion channels in planar lipid bilayers, to allow translocation. These are assumed to reseal themselves once the cytotoxic domain of the colicin has entered the cytoplasm. | |||
<ref> PMID: 15044477 </ref> | <ref> PMID: 15044477 </ref> | ||
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==Killing Activities== | ==Killing Activities== | ||
The cytotoxic activity of colE9 is DNase activity. <ref> PMID: 12804762 </ref> | The cytotoxic activity of colE9 is DNase activity. <ref> PMID: 12804762 </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. | |||
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/> | ||
Revision as of 17:52, 25 January 2011
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
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.
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. [2]
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.
To aid the colicin in crossing the inner membrane, the colicin has the ability to form ion channels in planar lipid bilayers, to allow translocation. These are assumed to reseal themselves once the cytotoxic domain of the colicin has entered the cytoplasm.
Killing ActivitiesKilling Activities
The cytotoxic activity of colE9 is DNase activity. [4] 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.
In response to the DNA damage by colE9, the E. coli cell initiates an SOS response, prior to cell death. [5]
ReferencesReferences
- ↑ 15044477
- ↑ Law CJ, Penfold CN, Walker DC, Moore GR, James R, Kleanthous C. OmpF enhances the ability of BtuB to protect susceptible Escherichia coli cells from colicin E9 cytotoxicity. FEBS Lett. 2003 Jun 19;545(2-3):127-32. PMID:12804762
- ↑ Mosbahi K, Walker D, Lea E, Moore GR, James R, Kleanthous C. Destabilization of the colicin E9 Endonuclease domain by interaction with negatively charged phospholipids: implications for colicin translocation into bacteria. J Biol Chem. 2004 May 21;279(21):22145-51. Epub 2004 Mar 23. PMID:15044477 doi:10.1074/jbc.M400402200
- ↑ Law CJ, Penfold CN, Walker DC, Moore GR, James R, Kleanthous C. OmpF enhances the ability of BtuB to protect susceptible Escherichia coli cells from colicin E9 cytotoxicity. FEBS Lett. 2003 Jun 19;545(2-3):127-32. PMID:12804762
- ↑ Mosbahi K, Walker D, Lea E, Moore GR, James R, Kleanthous C. Destabilization of the colicin E9 Endonuclease domain by interaction with negatively charged phospholipids: implications for colicin translocation into bacteria. J Biol Chem. 2004 May 21;279(21):22145-51. Epub 2004 Mar 23. PMID:15044477 doi:10.1074/jbc.M400402200