Materials and Methods:
Recombinant, nicked PA63 as well as LF from B. anthracis were obtained from List Biological Laboratories Inc. (Campbell, CA, U.S.A). One mg of lyophilized PA63 protein was dissolved …
Cell Culture, Cytoxicity Assay and Measurement of TNF-release:
…Cells were trypsinized and reseeded for at most 15-20 times. For cytotoxicity experiments, cells were seeded in 96-well-plates and incubated with PA63+ LF together with the respective heterocyclic azolopyridinium salt in serum-free medium. After the indicated incubation periods, the morphology of J774A.1 cells was visualized by using a Zeiss Axiovert 40CFl microscope (Oberkochen, Germany) with a Jenoptik progress C10 CCD camera (Jena, Germany). The cytotoxic effect caused by PA63/LF on this cell line was analyzed in terms of cell lysis. …
Membrane Translocation Assay:
The pH-dependent membrane translocation of LF through PA63-channels was investigated on the surface of intact J774.A1 cells as originally described earlier (1, 2). Cells were grown in 96-well-plates and incubated for 30 min at 37C in serum-free medium with bafilomycin A1 (100 nM). During this period, some cells were treated also with 100 M of either chloroquine-based heterocyclic azolopyridinium salts (HA substances). Subsequently, the cells were incubated for 30 min at 4C with PA63 (1 g/mL) plus LF (1 g/mL) to enable binding of these proteins to the cell surface. Thereafter, the medium was removed and cells were incubated for 5 min at 37C with acidic medium (pH 5.0, for control pH 7.5) containing the respective HA substance (100 M). The acidic medium was removed and cells were incubated at 37C in neutral medium containing bafilomycin A1 (100 nM) to prevent normal uptake of LF. Pictures were taken after 2 h and the toxin-induced cell lysis was analyzed exactly as described before.
Lipid Bilayer Experiments:
Black lipid bilayer experiments were performed as described previously [63] using a 1% solution of diphytanoyl phosphatidylcholine (Avanti Polar Lipids, Alabaster AL, U.S.A.) in n-decane as membrane forming lipid. The instrumentation consisted of a Teflon chamber with two aqueous compartments separated by a thin wall. The small circular whole between the two compartments had a surface area of about 0.4 mm2. The aqueous salt solutions were buffered with 10 mM MES, pH 6. All salts were obtained from Merck (Darmstadt, Germany). PA63 was added from concentrated stock solutions after the membrane had turned black, to the aqueous phase to one side (the cis-side) of the membrane. The PA-induced membrane conductance was measured after application of a …
Titration Experiments
The binding of heterocyclic azolopyridinium salts to PA63-channels was studied by titration experiments similar to those used previously to investigate binding of carbohydrates to the LamB-channel of Escherichia coli or binding of chloroquine or EF and LF, respectively, to C2II- and PA63-channels in single- or multi-channel experiments [27], [31], [33], [42], [64]. PA63-channels were reconstituted into lipid bilayer …
In most cases the different HA-substances caused full blockage the PA63-channels. In case of only partial blockage of the PA63-channels caused by a certain fraction of channels that did not respond to binding …
Author did not indicate which specific lethal factor was utilized. List Labs provides Product #172 (Anthrax Lethal Factor (LF), Recombinant from B. anthracis) and Product #169 (Anthrax Lethal Factor (LF-A), Recombinant from B. anthracis Native Sequence).