The N-terminal amino-latch region of hlg2 component of staphylococcal bi-component c-haemolysin is dispensable for prestem release to form b-barrel pores

The contribution of N-terminal regions of staphylococcal bi-component c-haemolysin toxin components to haemolytic activity towards human erythrocyte cells was investigated in this study. A deletion construct of N-terminal amino acids 1–10 of Hlg2 (Hlg2 DN10), which is the S-component protein of c-haemolysin, had little effect on its haemolytic activity, whereas N-terminal 1–11 amino acid deletion (Hlg2 DN11) significantly delayed haemolysis. Moreover, a deletion of N-terminal amino acids 1–17 of LukF, which is the F-component protein of c-haemolysin, increased its haemolytic activity in combination with either the wild-type or Hlg2 DN10. Unlike the N-terminal amino-latch region of staphylococcal a-haemolysin, which is a single component b-barrel pore-forming toxin, the N-terminal regions present in c-haemolysin components are dispensable for the haemolytic activity of the bi-component toxin. These results strengthen our recent proposal that staphylococcal bi-component c-haemolysin toxin uses an N-terminal amino-latch independent molecular switch for prestem release during the formation of b-barrel pores.