ACTINOBACILLUS-ACTINOMYCETEMCOMITANS LEUKOTOXIN FORMS LARGE-CONDUCTANCE, VOLTAGE-GATED ION CHANNELS WHEN INCORPORATED INTO PLANAR LIPID BILAYERS

Actinobacillus actinomycetemcomitans leukotoxin is a member of the bac terial RTX (repeats in toxin) toxin family, produced by a diverse grou p of Gram-negative pathogens. Members of this group of toxins, althoug h similar in sequence, differ in target cell specificity with Actinoba cillus actinomycetemcomitans leukotoxin demonstrating a unique species -and cell-type specificity. Purified A. actinomycetemcomitans leukotox in added to pre-formed POPE/POPS lipid bilayers showed no spontaneous incorporation (to concentrations of 250 ng/ml). Reproducible channel a ctivity was seen when the bilayer was reformed from lipid monolayers i n the presence of toxin (50 ng/ml) in one of the aqueous chambers. Con trol experiments with heat-inactivated toxin did not display channel a ctivity under the same experimental conditions. The channel behavior s howed a complex pattern of multiple conductance levels of 118, 262 and 406 pS in solutions containing 0.140 M NaCl. The first two states sho wed voltage-dependent channel gating with approximately equal but oppo site apparent,eating charges of 1.4 electrons. A model accounting for the multiple conducting states and gating properties is presented.