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A sequence‐specific function for the N‐terminal signal‐like sequence of the TonB protein

TonB is a proline‐rich protein which provides a functional link between the inner and outer membranes of Gram‐negative bacteria. TonB is anchored to the inner membrane via an N‐terminal signal‐like sequence and spans the periplasm, interacting with transport receptors in the outer membrane. We have investigated the role of the N‐terminal signal‐like peptide in TonB function. Replacement of the N‐terminal sequence with heterologous sequences indicates that it has at least three distinct rotes in TonB function: (i) to facilitate translocation of TonB across the cytoplasmic membrane; (ii) to anchor TonB to the cytoplasmic membrane; (iii) a sequence‐specific functional interaction with the ExbBD proteins.