View source for Colicin B

Colicin B is a type of [[Colicin]], a bacteriocin made by ''E. coli'' which acts against other nearby ''E. coli'' to kill them by forming a pore in the membrane, leading to depolarisation of the membrane which kills the cell. 

==Synthesis and release==

The operon for colicin B is encoded on a plasmid in the cytoplasm of the ''E. coli''. This operon also encodes its [[Colicin Immunity Protein]], [[Cbi]], to protect the membrane of the cell from the pore forming activities of the colicin, alongside a protein to aid the release of the colicin outside the cell. 

Once produced, the immunity protein inserts into the membrane to prevent pore formation.

==Mechanism of uptake==

The receptor binding domain of the colicin binds to the outer membrane receptor FepA on the target cell; it is a constitutively expressed protein parasitised by the colicin. The translocation domain then recruits proteins from the [[Ton]] system to translocate the protein across the membrane and into the cytoplasm.

==Killing Activities==

Colicin B has [[Pore Formation]] activities, whereby it inserts into the membrane of the targeted cell from the cytoplasm, and forms a pore. This causes depolarisation of the membrane, which is needed for the cell to synthesise ATP. Once this process is halted, the cell cannot survive and so dies.