AN ALPHA-HELICAL HYDROPHOBIC HAIRPIN AS A SPECIFIC DETERMINANT IN PROTEIN-PROTEIN INTERACTION OCCURRING IN ESCHERICHIA-COLI COLICIN-A AND COLICIN-B IMMUNITY SYSTEMS

A collection of chimeric pore-forming domains between colicins A and B was constructed to investigate the specific determinants responsible for recognition by the corresponding immunity proteins. The fusion sites in the hybrid proteins were positioned according to the three-dimensional structure of the soluble form of the colicin A pore-forming domain. The hydrophobic hairpin of colicin pore-forming domains, buried in the core of the soluble structure, was the main determinant recognized by the integral immunity proteins. The immunity protein function may require helix-helix recognition within the lipid bilayer.