title: Ion conductance of the stem of the anthrax toxin channel during lethal factor translocation.
abstract: The tripartite anthrax toxin consists of protective antigen, lethal factor (LF), and edema factor. PA63 (the 63-kDa, C-terminal part of protective antigen) forms heptameric channels in cell membranes that allow for the transport of LF and edema factor into the cytosol. These channels are mushroom shaped, with a ring of seven phenylalanine residues (known as the phenylalanine clamp) lining the junction between the cap and the stem. It is known that when LF is translocated through the channel, the phenylalanine clamp creates a seal that causes an essentially complete block of conduction. In order to examine ion conductance in the stem of the channel, we used Venus yellow fluorescent protein as a molecular stopper to trap LFN (the 30-kDa, 263-residue N-terminal segment of LF), as well as various truncated constructs of LFN, in mutant channels in which the phenylalanine clamp residues were mutated to alanines. Here we present evidence that ion movement occurs within the channel stem (but is stopped, of course, at the phenylalanine clamp) during protein translocation. Furthermore, we also propose that the lower region of the stem plays an important role in securing peptide chains during translocation.
authors.affiliation: Department of Physiology and Biophysics, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA. Electronic address: aviva.schiffmiller@phd.einstein.yu.edu.
authors.forename: Aviva
authors.initials: A
authors.lastname: Schiffmiller
authors.affiliation: Department of Physiology and Biophysics, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA.
authors.forename: Alan
authors.initials: A
authors.lastname: Finkelstein
mesh_terms: D019943:Amino Acid Substitution; D000942:Antigens, Bacterial / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001427:Bacterial Toxins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004553:Electric Conductivity; D007473:Ion Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008164:Luminescent Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary / Q000235:genetics; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism
chemical_list: D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D007473:Ion Channels; D008164:Luminescent Proteins; D011993:Recombinant Fusion Proteins; C030325:anthrax toxin; C054562:yellow fluorescent protein, Bacteria
keywords: conductance block; ion-conducting channels; phenylalanine clamp; protein translocation; single channels