Major transmembrane movement associated with colicin Ia channel gating

Colicin Ia forms channels in phospholipid bilayers as directed by voltage changes. The parts of the membrane involved during the opening and closing of channels were identified with the addition of streptavidin. Two transmembrane segments, upstream and downstream, were found to form in association with channel gating. The addition of streptavidin to the cis phase prevented channel opening but had no effect on the other opened channels thereby allowing a segment of the translocated protein to be a part of the upstream segment inserted into the bilayer.