Protein translocation through the anthrax toxin transmembrane pore is driven by a proton gradient.
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 (DeltapH, 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 (LFN) through the PA63 pore. DeltapH-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 phi clamp) drives translocation synergistically under a DeltapH. We propose that a Brownian ratchet mechanism proposed earlier for the phi clamp is cooperatively linked to a protonation-state, DeltapH-driven ratchet acting trans to the phi-clamp site. In a sense, the channel functions as a proton/protein symporter.
Krantz
Bryan A
BA
Department of Microbiology and Molecular Genetics, Harvard Medical School 200 Longwood Ave, Boston, MA 02115, USA.
Finkelstein
Alan
A
Collier
R John
RJ
D000818:Animals; D000942:Antigens, Bacterial / Q000235:genetics / Q000378:metabolism*; D001427:Bacterial Toxins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D008051:Lipid Bilayers / Q000378:metabolism; D008564:Membrane Potentials; D020673:Protein Renaturation; D021381:Protein Transport / Q000502:physiology*; D011522:Protons; D022161:Transport Vesicles / Q000378:metabolism
D000942:Antigens, Bacterial; D001427:Bacterial Toxins; D008051:Lipid Bilayers; D011522:Protons; C030325:anthrax toxin