ABSTRACT
Permeation of the cell wall membrane leading to cell death is a mechanism used by a large number of cytolytic polypeptides. The majority of these peptides can be classified into two main groups: (1) linear peptides, mostly helical, which do not contain cysteines, and (2) peptides with one or more disulfide bonds forming β-sheet or both β-sheet and α-helix structures (1). The most studied group contains host-defense short linear polypeptides (40 amino acids). They vary considerably in sequence, chain length, hydrophobicity, and overall distribution of charges. The list includes (1) cytolytic peptides that are toxic to bacteria only, such as cecropins, isolated from the cecropia moth (2), and magainins (3) and dermaseptins (4), both isolated from the skin of frogs; (2) cytolytic peptides that are selectively cytotoxic to mammalian cells but not to bacteria, such as δ-hemolysin isolated from Staphylococcus aureus (5); and (3) cytolytic peptides that are not cell-selective, such as the bee venom melittin (6) and the neurotoxin pardaxin (7-9), which lyse bacteria and mammalian cells. Table 1 shows as an example the sequences and sources of several cytolytic peptides.
