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À propos de : The Staphylococcal Leukocidin Bicomponent Toxin Forms Large Ionic Channels,        

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  • The Staphylococcal Leukocidin Bicomponent Toxin Forms Large Ionic Channels,
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  • The genes encoding the F and S components of a leukocidin, LukF (HlgB) and LukS (HlgC),a pore-forming binary toxin, were amplified from the Smith 5R strain of Staphylococcus aureus bothwith and without sequences encoding 3‘-hexahistidine tags. The His-tagged components were expressedin Escherichia coli and purified under nondenaturing conditions. In addition, the two unmodified proteinsand the His-tagged versions were produced in an E. coli cell-free in vitro transcription and translationsystem. An SDS-stable oligomer of approximately 200 kDa appeared when both components werecotranslated in the presence of rabbit erythrocyte membranes. Hemolytic activity of the combinedcomponents against rabbit erythrocytes was measured for both in vitro- and in vivo-produced polypeptides,yielding similar HC50 values of ∼0.14 μg/mL. The pore-forming properties of the recombinant leukocidinwere also investigated with planar lipid bilayers of diphytanoylphosphatidylcholine. Although leukocidinsand staphylococcal α-hemolysin share partial sequence identity and related folds, LukF and LukS producea pore with a unitary conductance of 2.5 nS [1 M KCl and 5 mM HEPES (pH 7.4)], which is more than3 times greater than that of α-hemolysin measured under the same conditions. Therefore, if the leukocidinpore were a cylinder, its diameter would be almost twice that of α-hemolysin. In addition, the leukocidinpore is weakly cation selective and exhibits gating at low positive potentials, while α-hemolysin is weaklyanion selective and gates only at high potentials. Taken together, these data suggest that the structure ofthe oligomeric pore formed by the leukocidin examined here has diverged significantly from that ofα-hemolysin.
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