title: Translocation trumps receptor binding in colicin entry into Escherichia coli.
abstract: Of the steps involved in the killing of Escherichia coli by colicins, binding to a specific outer-membrane receptor was the best understood and earliest characterized. Receptor binding was believed to be an indispensable step in colicin intoxication, coming before the less well-understood step of translocation across the outer membrane to present the killing domain to its target. In the process of identifying the translocator for colicin Ia, I created chimaeric colicins, as well as a deletion missing the entire receptor-binding domain of colicin Ia. The normal pathway for colicin Ia killing was shown to require two copies of Cir: one that serves as the primary receptor and a second copy that serves as translocator. The novel Ia colicins retain the ability to kill E. coli, even in the absence of receptor binding, as long as they can translocate via their Cir translocator. Experiments to determine whether colicin M uses a second copy of its receptor, FhuA, as its translocator were hampered by precipitation of colicin M chimaeras in inclusion bodies. Nevertheless, I show that receptor binding can be bypassed for killing, as long as a translocation pathway is maintained for colicin M. These experiments suggest that colicin M, unlike colicin Ia, may normally use a single copy of FhuA as both its receptor and its translocator. Colicin E1 can kill in the absence of receptor binding, using translocation through TolC.
authors.affiliation: Department of Physiology and Biophysics, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA. karen.jakes@einstein.yu.edu
authors.forename: Karen S
authors.initials: KS
authors.lastname: Jakes
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism* / Q000494:pharmacology; D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism*; D001692:Biological Transport; D003087:Colicins / Q000378:metabolism* / Q000494:pharmacology; D004926:Escherichia coli / Q000187:drug effects / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000378:metabolism*; D008958:Models, Molecular; D011485:Protein Binding
chemical_list: D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; D003087:Colicins; D029968:Escherichia coli Proteins; C050900:FhuA protein, E coli; D026901:Membrane Transport Proteins; C073126:tolC protein, E coli