Characterization of Molecular Properties of Pore-Forming Toxins with Planar Lipid Bilayers

Pore-forming toxins (PFTs) belong to the membrane-damaging toxins supergroup, a family of proteins already quite large but still quickly growing (1 ). PFT s are used by the bacteria to attack potentially harmful cells of the host, for example cells of the immune system, or to obtain nutrients, for example by lysing red blood cells (2 ). They produce well-defined pores in the plasma membrane of attacked cells, thus increasing their permeability to ions and small molecules. These exogenous channels can rupture small non-nucleated cells (e.g., red blood cells and platelets) via the so-called colloid-osmotic shock. In the case of large nucleated cells, for example, the leukocytes, they may trigger Ca^undefined+ entry followed by a number of secondary effects elicited by this messenger, leading finally to apoptosis and cell death. Besides being a very important pathogenic factor in a number of widespread diseases, bacterial PFT s are also finding new, and sometimes unexpected, applications. For example, they can be used to selectively permeabilize cells to molecules up to a certain size (the pore cutoff) for in vitro studies of cell functions (3 ,4 ), or to build immunotoxins or mitotoxins specifically directed against cancer cells (5 ,6 ), or even to construct new engineered single molecule biosensors for electronic devices (7 ).