Colicin Ia: Difference between revisions
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Colicin Ia is a type of [[Colicin]], a bacteriocin made by ''E. coli'' which acts against other nearby ''E. coli'' to kill them by forming a | Colicin Ia is a type of [[Colicin]], a bacteriocin made by ''E. coli'' which acts against other nearby ''E. coli'' to kill them by forming a voltage-dependent channel in the inner membrane of the cells that it targets. | ||
==Synthesis and release== | ==Synthesis and release== | ||
Colicin Ia is a 69kDa protein. | Colicin Ia is a 69kDa protein encoded on a high molecular weight plasmid<ref> PMID: 1943995 </ref> that is induced by the SOS system during stress<ref> PMID: 3531169 </ref>. The gene is tightly linked to its specific [[Colicin Immunity Protein]], [[Lia]], to protect the colicinogenic cell from the cytotoxic activity of the colicin<ref> PMID: 12423780 </ref>. The gene goes not encode a lysis protein, like [[Colicin V]] for its release from the cell, instead it uses export proteins already present to push itself out of the cell and not destroy it. | ||
==Mechanism of uptake== | ==Mechanism of uptake== | ||
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The flexible<ref> PMID: 15452437 </ref> N terminus of ColIa is responsible for binding to the colicin I receptor (Cir), which is a TonB-dependent transporter. Its normal function on ''E. coli'' is binding and transporting Fe<sup>3+</sup> across the outer membrane, but is parasitized by colicins for their transport and entry. When ColIa binds to Cir it results in a big conformational change, resulting in Cir being open and exposed extracellularly, with the ColIa R-domain positioned directly above it, bound at approximately 45<sup>o</sup> to the membrane. This results in the T and C domains remaining far above the membrane and away from the receptor. If Cir is indeed the molecule that transports ColIa across the membrane, this conformational change is that that would be required for penetration by the colicin<ref> PMID: 17464289 </ref>. | The flexible<ref> PMID: 15452437 </ref> N terminus of ColIa is responsible for binding to the colicin I receptor (Cir), which is a TonB-dependent transporter. Its normal function on ''E. coli'' is binding and transporting Fe<sup>3+</sup> across the outer membrane, but is parasitized by colicins for their transport and entry. When ColIa binds to Cir it results in a big conformational change, resulting in Cir being open and exposed extracellularly, with the ColIa R-domain positioned directly above it, bound at approximately 45<sup>o</sup> to the membrane. This results in the T and C domains remaining far above the membrane and away from the receptor. If Cir is indeed the molecule that transports ColIa across the membrane, this conformational change is that that would be required for penetration by the colicin<ref> PMID: 17464289 </ref>. | ||
The entry mechanism for ColIa into the periplasm after receptor binding is still unclear. The pair of α helices that separate the T and C domains from the R domain was suggested to allow ColIa to span the membrane, with the R domain being left outside the cell. The C domain is the only one expected to pass across the inner membrane and enter the cytoplasm<ref> PMID: 9729746 </ref>. Alternatively the 45<sup>o</sup> angle made with the membrane may allow the ColIa to search the surrounding regions for a co-transporter or other method of entry to the cell. | The entry mechanism for ColIa into the periplasm after receptor binding is still unclear. The pair of α helices that separate the T and C domains from the R domain was suggested to allow ColIa to span the membrane, with the R domain being left outside the cell. The C domain is the only one expected to pass across the inner membrane and enter the cytoplasm<ref> PMID: 9729746 </ref>. Alternatively the 45<sup>o</sup> angle made with the membrane may allow the ColIa to search the surrounding regions for a co-transporter or other method of entry to the cell. For killing by ColIa to be successful, Cir requires a functional [[TonB]] box sequence, as does ColIa, which implies that an interaction with TonB is required for uptake of ColIa<ref> PMID: 17464289 </ref>. | ||
ColIa has been shown to transport cargo proteins on its N terminus across the lipid bilayer when it penetrates the target cell. This transport uses the voltage across the bilayer to bring the folded proteins across the membrane<ref> PMID: 11830660 </ref>. | ColIa has been shown to transport cargo proteins on its N terminus across the lipid bilayer when it penetrates the target cell. This transport uses the voltage across the bilayer to bring the folded proteins across the membrane<ref> PMID: 11830660 </ref>. | ||
==Killing Activities== | |||
The [[Pore Formation]] domain, once it has translocated across the periplasmic space, inserts into the inner membrane of the target ''E. coli'' and forms a voltage-dependent ion channel that opens at a positive potential and closes at a negative potential, and conduct cations and anions<ref> PMID: 740032 </ref>. ColIa transfers a region of itself containing 4 α helices across the membrane as part of its gating<ref> PMID: 15702371 </ref>. | |||
The structural and mechanical sides of the pore formation by ColIa is an enigma; structurally there isn't enough protein to form such a pore, and mechanically the gating involves the transmembrane movement of a large portion of the protein, but it is unclear how this senses the voltage or forms the pore. | |||
==References== | |||
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