Colicin E1

Colicin E1 is a pore-forming bacteriocin, a bacterial protein capable of disrupting susceptible bacterial cell membranes. Its channel-forming region lies toward the C-terminus. The protein is distinct from the Colicin E1 plasmid, the DNA element associated with its production.

A 1983 experiment compared intact Colicin E1 with its roughly $20\mathrm{kDa}$ terminal fragment in artificial planar lipid bilayers. Both produced similar individual-channel and aggregate electrical behaviour, supporting localization of channel-forming function to that part of the protein.^[ref]

Both forms could associate with a lipid bilayer without an applied electric potential difference, while formation of conducting channels required the specified polarity of membrane potential. Attachment and channel opening are therefore distinguishable steps: seeing membrane-associated protein does not establish that an ion-conducting pore is open.^[ref]