title: Dynamic Phenylalanine Clamp Interactions Define Single-Channel Polypeptide Translocation through the Anthrax Toxin Protective Antigen Channel.
abstract: Anthrax toxin is an intracellularly acting toxin where sufficient detail is known about the structure of its channel, allowing for molecular investigations of translocation. The toxin is composed of three proteins, protective antigen (PA), lethal factor (LF), and edema factor (EF). The toxin's translocon, PA, translocates the large enzymes, LF and EF, across the endosomal membrane into the host cell's cytosol. Polypeptide clamps located throughout the PA channel catalyze the translocation of LF and EF. Here, we show that the central peptide clamp, the ϕ clamp, is a dynamic site that governs the overall peptide translocation pathway. Single-channel translocations of a 10-residue, guest-host peptide revealed that there were four states when peptide interacted with the channel. Two of the states had intermediate conductances of 10% and 50% of full conductance. With aromatic guest-host peptides, the 50% conducting intermediate oscillated with the fully blocked state. A Trp guest-host peptide was studied by manipulating its stereochemistry and prenucleating helix formation with a covalent linkage in the place of a hydrogen bond or hydrogen-bond surrogate (HBS). The Trp peptide synthesized with ʟ-amino acids translocated more efficiently than peptides synthesized with D- or alternating D,ʟ-amino acids. HBS stapled Trp peptide exhibited signs of steric hindrance and difficulty translocating. However, when mutant ϕ clamp (F427A) channels were tested, the HBS peptide translocated normally. Overall, peptide translocation is defined by dynamic interactions between the peptide and ϕ clamp. These dynamics require conformational flexibility, such that the peptide productively forms both extended-chain and helical states during translocation.
authors.affiliation: Department of Microbial Pathogenesis, School of Dentistry, University of Maryland, Baltimore, 650 W, Baltimore Street, Baltimore, MD 21201, USA.
authors.forename: Koyel
authors.initials: K
authors.lastname: Ghosal
authors.affiliation: Department of Pathology, Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA.
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Colby
authors.affiliation: Department of Microbial Pathogenesis, School of Dentistry, University of Maryland, Baltimore, 650 W, Baltimore Street, Baltimore, MD 21201, USA.
authors.forename: Debasis
authors.initials: D
authors.lastname: Das
authors.affiliation: Department of Chemistry, New York University, New York, NY 10003, USA.
authors.forename: Stephen T
authors.initials: ST
authors.lastname: Joy
authors.affiliation: Department of Chemistry, New York University, New York, NY 10003, USA.
authors.forename: Paramjit S
authors.initials: PS
authors.lastname: Arora
authors.affiliation: Department of Microbial Pathogenesis, School of Dentistry, University of Maryland, Baltimore, 650 W, Baltimore Street, Baltimore, MD 21201, USA. Electronic address: bkrantz@umaryland.edu.
authors.forename: Bryan A
authors.initials: BA
authors.lastname: Krantz
mesh_terms: D000942:Antigens, Bacterial / Q000235:genetics / Q000378:metabolism; D001427:Bacterial Toxins / Q000235:genetics / Q000378:metabolism; D004252:DNA Mutational Analysis; D011487:Protein Conformation; D025941:Protein Interaction Mapping; D021381:Protein Transport
chemical_list: D000942:Antigens, Bacterial; D001427:Bacterial Toxins; C030325:anthrax toxin
keywords: Bacillus anthracis; anthrax toxin; electrophysiology; peptide clamp; protective antigen