title: Retrocyclins kill bacilli and germinating spores of Bacillus anthracis and inactivate anthrax lethal toxin.
abstract: Theta-defensins are cyclic octadecapeptides encoded by the modified alpha-defensin genes of certain nonhuman primates. The recent demonstration that human alpha-defensins could prevent deleterious effects of anthrax lethal toxin in vitro and in vivo led us to examine the effects of theta-defensins on Bacillus anthracis (Sterne). We tested rhesus theta-defensins 1-3, retrocyclins 1-3, and several analogues of RC-1. Low concentrations of theta-defensins not only killed vegetative cells of B. anthracis (Sterne) and rendered their germinating spores nonviable, they also inactivated the enzymatic activity of anthrax lethal factor and protected murine RAW-264.7 cells from lethal toxin, a mixture of lethal factor and protective antigen. Structure-function studies indicated that the cyclic backbone, intramolecular tri-disulfide ladder, and arginine residues of theta-defensins contributed substantially to these protective effects. Surface plasmon resonance studies showed that retrocyclins bound the lethal factor rapidly and with high affinity. Retrocyclin-mediated inhibition of the enzymatic activity of lethal factor increased substantially if the enzyme and peptide were preincubated before substrate was added. The temporal discrepancy between the rapidity of binding and the slowly progressive extent of lethal factor inhibition suggest that post-binding events, perhaps in situ oligomerization, contribute to the antitoxic properties of retrocyclins. Overall, these findings suggest that theta-defensins provide molecular templates that could be used to create novel agents effective against B. anthracis and its toxins.
authors.affiliation: Department of Medicine, David Geffen School of Medicine, University of California-Los Angeles, 10833 LeConte Avenue, Los Angeles, CA 90095, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.forename: Chandrika
authors.initials: C
authors.lastname: Mulakala
authors.forename: Sabrina C
authors.initials: SC
authors.lastname: Ward
authors.forename: Grace
authors.initials: G
authors.lastname: Jung
authors.forename: Hai
authors.initials: H
authors.lastname: Luong
authors.forename: Duy
authors.initials: D
authors.lastname: Pham
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Waring
authors.forename: Yiannis
authors.initials: Y
authors.lastname: Kaznessis
authors.forename: Wuyuan
authors.initials: W
authors.lastname: Lu
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Bradley
authors.forename: Robert I
authors.initials: RI
authors.lastname: Lehrer
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000881:Anthrax / Q000517:prevention & control*; D000942:Antigens, Bacterial; D001408:Bacillus anthracis / Q000187:drug effects* / Q000235:genetics; D001427:Bacterial Toxins / Q000037:antagonists & inhibitors*; D015169:Colony Count, Microbial; D023082:Defensins / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D007700:Kinetics; D017737:Macrophages, Peritoneal / Q000187:drug effects / Q000382:microbiology; D051379:Mice; D008826:Microbial Sensitivity Tests; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D013170:Spores / Q000187:drug effects*; D020349:Surface Plasmon Resonance
chemical_list: D000942:Antigens, Bacterial; D001427:Bacterial Toxins; D023082:Defensins; C030325:anthrax toxin; C450142:theta-defensin