Tc toxins are widely distributed among different gram-negative and gram-positive 
bacteria, where they act as pathogenicity factors. The toxins are composed of 
different components that form oligomers for biological activity. Lipid bilayer 
experiments were performed with the TcdA1 component of the Tc toxin from 
Photorhabdus luminescens, which preferentially kills insects by actin 
polymerization. TcdA1 was able to increase the specific conductance of 
artificial lipid bilayer membranes by the formation of ion-permeable channels. 
The channels had on average a single-channel conductance of 125 pS in 150 mM KCl 
and were found to be cation selective. The single-channel conductance of the 
TcdA1-channels was only moderately dependent on the bulk aqueous KCl 
concentration, which indicated point-charge effects on the channel properties. 
Experiments to study the voltage dependence of the TcdA1 channel demonstrated 
that it is reconstituted in a fully oriented way when it is added to only one 
side of the lipid bilayer membrane. A combination of biologically active 
components (TccC3) and a possible chaperone (TcdB2) blocked the TcdA1-mediated 
conductance efficiently in a dose-dependent manner when they were added to the 
cis side of the membrane. The half-saturation constant for binding of 
TcdB2-TccC3 to TcdA1 is in the low nanomolar range.