EFFECT OF ANTHRAX TOXINS LETHAL FACTOR ON ION CHANNELS FORMED BY THE PROTECTIVE ANTIGEN

Protective antigen (PA), a component of anthrax toxin, mediates transl ocation of the toxin's lethal and edema factors (LF and EF, respective ly) to the cytoplasm, via a pathway involving their release from an ac idic intracellular compartment. PA(63), a 63-kDa proteolytic fragment of PG can be induced to form ion-conductive channels in the plasma mem brane of mammalian cells by acidification of the medium. These channel s are believed to be comprised of dodecyl sulfate resistant oligomers (heptameric rings) of PA(63) seen by electron microscopy of the purifi ed protein. Here we report that the PA(63)-mediated efflux of Rb-86(+) from preloaded CHO-K1 cells under acidic conditions is strongly inhib ited (greater than or equal to 70%) by LF or LF(N), a PA-binding fragm ent of LF. Control proteins caused no inhibition, Evidence is presente d that the inhibition involves partial blockage of ion conductance by the PA(63), channel. Also, oligomer formation is slowed somewhat by LF at pH values near the pH threshold of channel formation (pH similar t o 5.3), suggesting that channel formation may also be retarded under t hese conditions. The relevance of these results to the location of the LF-binding site on PA(63) and the mechanism of LF and EF translocatio n is discussed.