Distinct regions of the colicin A translocation domain are involved in the interaction with TolA and TolB proteins upon import into Escherichia coli

Abstract

Group A colicins need proteins of the Escherichia coli envelope Tol complex (TolA, TolB, TolQ and TolR) to reach their cellular target. The N‐terminal domain of colicins is involved in the import process. The N‐terminal domains of colicins A and E1 have been shown to interact with TolA, and the N‐terminal domain of colicin E3 has been shown to interact with TolB. We found that a pentapeptide conserved in the N‐terminal domain of all group A colicins, the ‘TolA box’, was important for colicin A import but was not involved in the colicin A–TolA interaction. It was, however, involved in the colicin A–TolB interaction. The interactions of colicin A N‐terminal domain deletion mutants with TolA and TolB were investigated. Random mutagenesis was performed on a construct allowing the colicin A N‐terminal domain to be exported in the bacteria periplasm. This enabled us to select mutant protein domains unable to compete with the wild‐type domain of the entire colicin A for import into the cells. Our results demonstrate that different regions of the colicin A N‐terminal domain interact with TolA and TolB. The colicin A N‐terminal domain was also shown to form a trimeric complex with TolA and TolB.