Association of listeriolysin O with the cell surface of Listeria monocytogenes.

The single amino acid substitutions were created in the C-terminal region of listeriolysin O. Mutations cys484 to Ala and Ser showed a close relationship between surface activity of LLO and presence of cysteine in this polipeptide. We demonstrated that Cys484 is necessary for surface haemolytic activity. LLO with Cys484 is strongly connected to the surface of the cell but LLO Ala484 or Ser484 is easy removed by the washing. Listeriolysins O secreted by the mutants were active at low pH and inhibited by cholesterol. Mutated hemolysin was still active at high pH without cysteine in reaction mixture whereas wild hemolysin was not. Surface haemolytic activity was blocked in Ala484 strain at high pH. The finding that mutants Ala484 and Ser484 have changed surface activity suggests that cysteine in LLO may play a significant role for surface haemolytic activity necessary in late stages of Listeria monocytogenes cell cycle.