SECONDARY STRUCTURE OF ANTHRAX LETHAL TOXIN PROTEINS AND THEIR INTERACTION WITH LARGE UNILAMELLAR VESICLES - A FOURIER-TRANSFORM INFRARED-SPECTROSCOPY APPROACH

Attenuated total reflection Fourier transform infrared spectroscopy ha s been used to study the secondary structure of anthrax lethal toxin p roteins: protective antigen (PA) and lethal factor (LF), as a function of pH in the absence and in the presence of phospholipid vesicles. We first characterized the binding of LF and PA to the lipid membrane an d demonstrated the strong pH dependence of the association of PA and L F to the lipid bilayer as well as the effect of pH neutralization on t his binding. Binding of LF to the lipid membrane can be, at least part ially, reversed when the pH is brought to neutral whereas in the same conditions PA binding is irreversible. Characterization of the conform ational changes undergone by PA and LF upon pH lowering, lipid binding , and, in the case of LF, reversal of binding was carried out (i) by d etermining the secondary structure of the proteins and (ii) by evaluat ing their ability to undergo an hydrogen/deuterium exchange.