Effect of pH on stability of anthrax lethal factor: Correlation between denaturation and activity

Anthrax is caused by Gram positive bacterium Bacillus anthracis. Pathogenes is is result of production of three protein components, protective antigen (PA), lethal factor (LF), and edema factor (EF). PA in combination with LF (lethal toxin) is lethal to animals, while PA in combination with EF (edema toxin), causes edema. PA, LF, and EF are very thermolabile. Differential s canning calorimetry (DSC) was used to unravel the energetics of LF denatura tion as a function of pH ranging from 7.8 to 5.5. Transition temperature (T -m) of LF was found to be approximate to 42 degreesC and onset of denaturat ion occurs at approximate to 30 degreesC. The ratio of calorimetric to van' t Hoff's enthalpy was nearly equal to unity at pH 7.0, indicative of presen ce of single structural domain in LF at pH 7.0, unlike PA which has been st ructurally observed to consist of 4 domains. It was found by cytotoxicity s tudies using J774A.1 macrophage like cells that LF was most stable at pH si milar to6.5. This paper reports for the first time the denaturation of LF a t different pH values at 37 degreesC and tries to establish a correlation b etween denaturation and loss of LF activity at different pH values. (C) 200 1 Academic Press.