Translocation of a functional protein by a voltage-dependent ion channel

The voltage-dependent gating of the colicin channel involves a substantial structural rearrangement that results in the transfer of about 35% of the 200 residues in its pore-forming domain across the membrane. This transfer appears to represent an unusual type of protein translocation that does not depend on a large, multimeric, protein pore. To investigate the ability of this system to transport arbitrary proteins, we made use of a pair of strongly interacting proteins, either of which could serve as a translocated cargo or as a probe to detect the other. Here we show that both an 86-residue and a 134-residue hydrophilic protein inserted into the translocated segment of colicin A are themselves translocated and are functional on the trans side of the bilayer. The disparate features of these proteins suggest that the colicin channel has a general protein translocation mechanism.