Protein translocation through the anthrax toxin transmembrane pore is driven by a proton gradient

Bryan A. Krantz, Alan Finkelstein, R. John Collier

Research output: Contribution to journalArticlepeer-review

155 Scopus citations


Protective antigen (PA) from anthrax toxin assembles into a homoheptamer on cell surfaces and forms complexes with the enzymatic components: lethal factor (LF) and edema factor (EF). Endocytic vesicles containing these complexes are acidified, causing the heptamer to transform into a transmembrane pore that chaperones the passage of unfolded LF and EF into the cytosol. We show in planar lipid bilayers that a physiologically relevant proton gradient (ΔpH, where the endosome is acidified relative to the cytosol) is a potent driving force for translocation of LF, EF and the LF amino-terminal domain (LF N) through the PA63 pore. ΔpH-driven translocation occurs even under a negligible membrane potential. We found that acidic endosomal conditions known to destabilize LFN correlate with an increased translocation rate. The hydrophobic heptad of lumen-facing Phe427 residues in PA (or φ clamp) drives translocation synergistically under a ΔpH. We propose that a Brownian ratchet mechanism proposed earlier for the φ clamp is cooperatively linked to a protonation-state, ΔpH-driven ratchet acting trans to the φ-clamp site. In a sense, the channel functions as a proton/protein symporter.

Original languageEnglish (US)
Pages (from-to)968-979
Number of pages12
JournalJournal of Molecular Biology
Issue number5
StatePublished - Feb 3 2006


  • Planar bilayers
  • Protein unfolding
  • Proton gradient
  • Translocase
  • Translocation

ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology


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