Anthrax-toxin-mediated delivery of a 19 kDa antigen of Mycobacterium tuberculosis into the cytosol of mammalian cells

PA63, the proteolytically activated 63 kDa fragment of protective antigen ( PA, 83kDa), mediates translocation of lethal factor (LF) and oedema factor into the cytosol. The N-terminal 254 amino acids of LF (LFn) are required f or binding to PA63 and mediating translocation of active ligands fused to e ither the N- or C-terminus. Here we report translocation of a 19 kDa antige n of Mycobocterium tuberculosis into the cytosol of mammalian cells when fu sed to the C-terminus of LFn (LFn-19kDa). The fusion protein was non-toxic to J774A.1 macrophage cells in combination with PA and retained the ability to bind to PA63 when incubated with Chinese hamster ovary K1 cells. The da ta show the efficacy of anthrax toxin to mediate translocation of M, tuberc ulosis antigens into the cytosol of mammalian cells and may prove useful in delivering proteins and peptides carrying immunodominant mycobacterial ant igens into the cytosol.