Colicin A binds to a novel binding site of TolA in the Escherichia coli periplasm

Colicins are protein antibiotics produced by Escherichia coli to kill closely related non-identical competing species. They have taken advantage of the promiscuity of several proteins in the cell envelope for entry into the bacterial cell. The Tol–Pal system comprises one such ensemble of periplasmic and membrane-associated interacting proteins that links the IM (inner membrane) and OM (outer membrane) and provides the cell with a structural scaffold for cell division and energy transduction. Central to the Tol–Pal system is the TolA hub protein which forms protein–protein interactions with all other members and also with extrinsic proteins such as colicins A, E1, E2–E9 and N, and the coat proteins of the Ff family of filamentous bacteriophages. In the present paper, we review the role of TolA in the translocation of colicin A through the recently determined crystal structure of the complex of TolA with a translocation domain peptide of ColA (TA_53–107), we demonstrate that TA_53–107 binds to TolA at a novel binding site and compare the interactions of TolA with other colicins that use the Tol–Pal system for cell entry substantiating further the role of TolA as a periplasmic hub protein.