STRUCTURE AND DYNAMICS OF THE COLICIN-E1 CHANNEL

The toxin‐like and bactericidal colicin E1 molecule is of interest for problems of toxin action, polypeptide translocation across membranes, voltage‐gated channels, and receptor function. Colicin E1 binds to a receptor in the outer membrane and is translocated across the cell envelope to the inner membrane. Import of the colicin channel‐forming domain into the inner membrane involves a translocation‐competent intermediate state and a membrane potential‐dependent movement of one third to one half of the channel peptide into the membrane bilayer. The voltage‐gated channel has a conductance sufficiently large to depolarize the Escherichia coli cytoplasmic membrane. Amino acid residues that affect the channel ion selectivity have been identified by site‐directed mutagenesis. The colicin E1 channel is one of a few membrane proteins whose secondary structures in the membrane, predominantly α‐helix, have been determined by physico‐chemical techniques. Hypotheses for the identity of the trans‐membrane helices, and the mechanism of binding to the membrane, are influenced by the solved crystal structure of the soluble colicin A channel peptide. The protective action of immunity protein is a unique aspect of the colicin problem, and information has been obtained, by genetic techniques, about the probable membrane topography of the imm gene product. Copyright © 1990, Wiley Blackwell. All rights reserved