Pore-Forming Colicins: Unusual Ion Channels – Unusually Regulated

Abstract

Colicins are toxins released by plasmid carrying Escherichia coli bacteria in order to kill bacteria not carrying the same plasmid. This selection is achieved since the plasmid bearing cells have an immunity protein that protects them from their own specific colicin. Colicins kill by peptidoglycan synthesis inhibition, nuclease digestion or pore formation. This review describes how the pore-forming colicins function, with reference to other types as needed. The function involves binding to target cells, translocation across the outer membrane and periplasm, insertion into the inner membrane and voltage gated pore formation. Due to this unusual pathway, the pores have an unusual and minimalist mode of pore formation that is still not fully defined. The immunity protein is an integral membrane protein of the inner membrane, which prevents formation of the open pore and thus protects the cell. Models for the interaction with the colicin pore are discussed which also give insights into protein-protein interactions in the lipid bilayer.